
Glass. 
Book 










T 



AN 



INQUIRY 



INTO THE 



HUMAN MIND. 



AN 



INQUIRY 



INTO THE 



HUMAN MIND, 



ON THE PRINCIPLES OP 



COMMON SENSE 



THOMAS REID, D. D, 
■MMf»* jo ' 

PROFESSOR OF MORAL FHlLOSjOF-HY IN THE UNIVERSITY 
OF GLASGOW. 



The Inspiration of the Almighty giveth them Understanding. — Job. 



EDINBURGH: 

PRINTED FOR STIRLING & SLADE, 

AND 

OGLE, ALLARDICE & THOMSON. 

1819. 



31533 

i Iz 

if [1 



UBRAI 

JOFCOBG1 



W* FALCONER, PRINTER, 
GLASGOW. 



TO 



THE RIGHT HONOURABLE 



JAMES, EARL OF FINDLATER AND 
SEAFIELD, 

Chancellor of the University of Old, Aberdeen. 
My Lord, 



Though I apprehend that there are things new 
and of some importance, in the following inquiry, 
it is not without timidity that I have consented 
to the publication of it. The subject has been 
canvassed by men of very great penetration and 
genius : for who does not acknowledge Des 
Cartes, Malebranche, Locke, Berkeley, and 
Hume, to be such ? A view of the human under- 
standing, so different from that which they have 
exhibited, will, no doubt, be condemned by many 
without examination, as proceeding from teme- 
rity and vanity. 



VI DEDICATION. 

But I hope the candid and discerning Few, 
who are capable of attending to the operations 
of their own minds, will weigh deliberately what 
is here advanced, before they pass sentence upon 
it. To such I appeal, as the only competent 
judges. If they disapprove, 1 am probably in 
the wrong, and shall be ready to change my opin- 
ion upon conviction. If they approve, the Many 
will at last yield to their authority, as they always 
do. 

However contrary my notions are to those of 
the writers I have mentioned, their speculations 
have been of great use to me, and seem even to 
point out the road which I have taken : and 
your Lordship knows, that the merit of useful 
discoveries is sometimes not more justly due to 
those that have hit upon them, than to others 
that have ripened them, and brought them to the 
birth. 

I acknowledge, my Lord, that I never thought 
of calling in question the principles commonly 
received with regard to the human understand, 
ing, until the Treatise of Human Nature was pub- 
lished in the year 1739. The ingenious author 
of that treatise, upon the priciples of Locke, 
who was no sceptic, hath butf t a system of seep- 



DEDICATION. Vll 

ticism, which leaves no ground to believe any 
one thing rather than its contrary. His reason- 
ing appeared to me to bejust: there was therefore 
a necessity to call in question the principles upon 
which it was founded, or to admit the conclu- 
sion. 

But can any ingenuous mind admit this scep- 
tical system without reluctance? I truly could 
not, my Lord: for I am persuaded, that absolute 
scepticism is not more destructive of the faith of 
a Christian, than of the science of a philosopher, 
and of the prudence of a man of common under- 
standing, I am persuaded, that the unjust live 
by faith as well as the just; that, if all belief could 
be laid aside, piety, patriotism, friendship, pa- 
rental affection, and private virtue, would appear 
as ridiculous as knight-errantry ; and that the 
pursuits of pleasure, of ambition, and of avarice, 
must be grounded upon belief, as well as those 
that are honourable or virtuous. 

The day-labourer toils at his work, in the be- 
lief that he shall receive his wages at night ; and 
if he had not this belief lie would not tod. We 
may venture to say, that even the author of this 
sceptical system, wrote it in the belief that it 
should be read and regarded. I hope he wrote 



Vlll DEDICATION. 

it in the belief also, that it would be useful tq 
mankind : and perhaps it may prove so at last. 
For I conceive the sceptical writers to be a set 
of men, whose business it is to pick holes in the 
fabric of knowledge wherever it is weak and 
faulty ; and when these places are properly re- 
paired, the whole building becomes more firm 
and solid than it was formerly. 

For my own satisfaction, I entered into d, 
serious examination of the principles upon which 
this sceptical system is built ; and was not a little 
surprised to find, that, it leans with its whole 
weight upon a hypothesis, which is ancient in- 
deed, and hath been very generally received by 
philosophers, but of which I could find no solid 
proof. The hypothesis I mean, is, That nothing 
is perceived but what is in the mind which per- 
ceives it : That we do not really perceive things 
that are external, but only certain images and 
pictures of them imprinted upon the mind, which 
are called impressions and ideas. 

If this be true ; supposing certain impressions 
and ideas to exist in my mind, I cannot, from 
their existence, infer the existence of any thing 
else : my impressions and ideas are the only ex- 
istences of which I can have any knowledge or 



DEDICATION. IX 

conception ; and they are such fleeting and tran- 
sitory beings, that they can have no existence at 
all, any longer than I am conscious of them. So 
that, upon this hypothesis, the whole universe 
about me, bodies and spirits, sun, moon, stars, 
and earth, friends and relations, all things with- 
out exception, which I imagined to have a per- 
manent existence, whether I thought of them or 
not, vanish at once j 

And, like the baseless fabric of a vision, 
Leave not a track behind. 

I thought it unreasonable, my Lord, upon 
the authority of philosophers, to admit a hypo- 
thesis, which, in my opinion, overturns all philo- 
sophy, all religion and virtue, and all common 
sense : and finding that all the systems concern- 
ing the human understanding which I was ac- 
quainted with, were built upon this hypothesis, I 
resolved to inquire into this subject anew, with- 
out regard to any hypothesis. 

What I now humbly present to your Lord- 
ship, is the fruit of this inquiry, so far only as it 
regards the five senses ; in which I claim no 
other merit, than that of having given great at- 
tention to the operations of my own mind, and 
of having expressed, with all the perspicuity J 



X DEDICATION. 

was able, what I conceive every man, who gives 
the same attention, will feel and perceive. The 
productions of imagination, require a genius 
which soars above the common rank ; but the 
treasures of knowledge are commonly buried 
deep, and may be reached by those drudges who 
can dig with labour and patience, though they 
have not wings to fly. The experiments that were 
to be made in this investigation suited me, as 
they required no other expence, but that of time 
and attention, which I could bestow. The lei- 
sure of an academical life, disengaged from the 
pursuits of interest and ambition ; the duty of 
my profession, which obliged me to give prelec- 
tions on these subjects to the youth ; and an 
early inclination to speculations of this kind,— 
have enabled me, as I flatter myself, to give a 
more minute attention to the subject of this in- 
quiry, than has been given before. 

My thoughts upon this subject were, a good 
many years ago, put together in another form, 
for the use of my pupils, and afterwards were 
submitted to the judgment of a private philoso- 
phical society, of which I have the honour to be 
a member. A great part of this inquiry was 
honoured even by your Lordship's perusal. And 
the encouragement which you, my Lord, and 



DEDICATION. XI 

others, whose friendship is my boast, and whose 
judgment I reverence, were pleased to give me, 
counterbalance my timidity and diffidence, and 
determined me to offer it to the public. 

If it appears to your Lordship to justify the 
common sense and reason of mankind, against 
the sceptical subtilties which, in this age, have 
endeavoured to put them out of countenance ; if 
it appears to throw any new light upon one of 
the noblest parts of the divine workmanship ; 
your Lordship's respect for the arts and sciences, 
and your attention to every thing which tends to 
the improvement of them, as well as to every 
thing else that contributes to the felicity of your 
country, leave me no room to doubt of your fa- 
vourable acceptance of this essay, as the fruit of 
my industry in a profession wherein I was ac- 
countable to your Lordship ; and as a testimony 
of the great esteem and respect wherewith I have 
the honour to be, 

My Lord, 
Your Lordship's most obliged, 

and most devoted servant, 
THO. REID. 



CONTENTS, 

CHAP. I. 
INTRODUCTION. 

Sect. m Page 

1. The importance of the subject, and the means of 

prosecuting it, . ... 17 

2. The impediments to our knoxdedge of the mind, 20 

3. The present state of this part of philosophy. Of 

Des Cartes, Malebranche, and Locke, . 26 

4. Apology for those philosophers, . . .31 

5. Of Bishop Berkeley — the Treatise of Human Na- 

ture — and of Scepticism, . . 33 

6. Of the Treatise of Human Nature, . . 37 

7. The system of all these authors is the same, and 

leads to scepticism, . . . 39 

S. We ought not to despair of a better, . . 41 

CHAP. II. 

OF SMELLING. 

Sect. 

1 . The order of proceeding. Of the medium and 

organ of Smell, . . . . . 44 

2. The sensation considered abstractly, . . 46 

3. Sensation and remembrance natural priaci pics of 

belief, 48 

4. Judgment and belief in some cases precede simple 

apprehension, . . 52 

-5. Two theories of the nature of belief refuted. — 

Conclusions from what hath been said. , 53 



XIV CONTENTS. 

Sect. Page 

6. Apology for metaphysical absurdities. Sensations 

without a sentient, a consequence of the theory 

of ideas. Consequences of this strange opinion, 57 

7. The conception and belief of a sentient being or 

mind, is suggested by our constitution. The 
notion of relations not always got by compar- 
ing the related ideas, . . . . 65 

8. There is a quality or virtue in bodies, which we 

call their smell. How this is connected in the 
imagination with the sensation, . 69 

9. That there is a principle in human nature, from 

which the notion of this, as well as all other 
natural virtues or causes, is derived, . 72 

1 0. Whether in sensation the mind is active or passive ? 78' 



CHAP. III. 
OF TASTING. 81 

CHAP. IV. 

OF HEARING. 

Sect. 

1. Variety of sounds. Their place and distance 

learned by custom, without reasoning, , 87 

2. Of natural language, . . . . .90 

CHAP. V. 
OF TOUCH, 

Sect. 
1. Of heat and cold, . * * • 96 



CONTENTS. XV 

Sect. Page 

2. Of hardness and softness, .... 99 

3. Of natural signs, . . . . . 10£ 

4. Of hardness and other -primary qualities, . 110 

5. Of extension, 112 

6. Of extension, . . . . . .117 

7. Of the existence of a material world, . . 121 

8. Of the systems of philosophers concerning the 

senses* 131 



CHAP. VI. 



OF SEEING. 

Sect. 

1. The excellence and dignity of this faculty, 13& 

2. Sight discovers almost nothing which the blind may 

not comprehend. The reason of this, . 141 

3. Of the visible appearance of objects, . . 148 

4. That colour is a quality of bodies, not a sensation 

of the mind, . . . . . .153 

5. An inference from the preceding* . . .158 

6. That none of our sensations are resemblances of 

any of the qualities of bodies, . . .163 

7. Of visible fgure and extension, . . .172 

8. Some queries concerning visible figure answered, 177 

9. Of the geometry of visibles, . . . 187 

10. Of the parallel motion of the eyes, . . 203 

11. Of our seeing objects erect by inverted images, 208 

12. The same subject continued, . . . 217 

1 3. Of seeing objects single with two eyes, . .239 

14. Of the laws of vision in brute animals, . 250 

1 5. Squinting considered hypotJietically, . . 205 



XVI CONTENTS. 

Sect. Page 

16'. Facts relating to squinting, . . \ 270 

17. Of the effect of custom in seeing objects single, 275 

18. Of Dr. Porterf eld's account of single and double 
vision, 285 

1 9. Of JJr. Brigg's theory, and Sir Isaac NewtOJis 

conjecture on this subject, . • . . 290 

20. Of perception in general, .... 305 

2 1 . Of the process of Nature in perception, . 317 

22. Of the signs by which we learn to perceive dis- 

tance from the eye, * 325 

23. Of the signs used in other acquired perceptions, 343 

24. Of the analogy between perception, and the credit 

we give to human testimony, . . .347 

CHAP. VII. 

CONCLUSION. 

Containing Befections upon the opinions of Philoso- 
phers on this subject, . * . . 371 



AN 



INQUIRY 



INTO THE 



HUMAN MIND. 



CHAP. L 

INTRODUCTION. 

SECT. I. 

The importance of the subject, and the means of 
prosecuting it. 

The fabric of the Human Mind is curious and 
wonderful, as well as that of the human body. 
The faculties of the one are with no less wisdom 
adapted to their several ends, than the organs of 
the other. Nay, it is reasonable to think, that as 
the mind is a nobler work, and of a higher order 
than the body, even more of the wisdom and skill 
of the Divine Architect hath been emploved ia 



18 OF THE HUMAN MIND. [CHAP. 1. 

worthy of inquiry on its own account, but still 
more worthy on account of the extreme influence 
which the knowledge of it hath over every other 
branch of science. 

In the arts and sciences which have least con- 
nection with the mind, its faculties are the en- 
gines which we must employ; and the better we 
understand their nature and use, their defects 
and disorders, the more skilfully we shall apply 
them, and with the greater success. But in the 
noblest arts, the mind is also the subject upon 
which we operate. The painter, the poet, the 
actor, the orator, the moralist, and the statesman, 
attempt to operate upon the mind in different 
ways, and for different ends; and they succeed 
according as they touch properly the strings of 
the human frame. Nor can their several arts ever 
■.stand on a solid foundation, or rise to the dignity 
■of science, until they are built on the principles 
of the human constitution. 

Wise men now agree, or ought to agree in 
this, that there is but one wav to the knowledge 
of Nature's works; the way of observation and 
experiment. By our constitution, we have a 
strong propensity to trace particular facts and 
observations to general rules, and to apply such 
general rules to account for other effects, or to 
direct us in the production of them. This pro- 
cedure of the understanding is familiar to every 
human creature in the common affairs of life, and 
it is the only one by which any real discovery in 
philosophy can be made. 



S£€T. 1.] INTRODUCTION. 19 

The man who first discovered that cold freezes 
water, and that heat turns it into vapour, pro- 
ceeded on the same general principles, and in 
the same method by which Newton discovered 
the law of gravitation, and the properties of light. 
His regulce philosophandi are maxims of common 
sense, and are practised every day in common 
life; and he who philosophizes by other rules, 
either concerning the material system, or con- 
cerning the mind, mistakes his aim. 

Conjectures and theories are the creatures of 
men, and will always be found very unlike the 
creatures of God. If we would know the works 
of God, we must consult themselves with atten- 
tion and humility, without daring to add any 
thing of ours to what they declare. A just in- 
terpretation of nature is the only sound and or- 
thodox philosophy : whatever w r e add of our own, 
is apocryphal, and of no authority. 

All our curious theories of the formation of the 
earth, of the generation of animals, of the origin 
of natural and moral evil, so far as they go be- 
yond a just induction from facts, are vanity and 
folly, no less than the vortices of Des Cartes, 
or the Archaeus of Paracelsus. Perhaps the 
philosophy of the mind hath been no less adul- 
terated by theories, than that of the material sys- 
tem. The theory of ideas is indeed very ancient, 
and hath been very universally received; but as 
neither of these titles can give it authenticity, 
they ought not to screen it from a free and can- 
did examination -, especially in this age, when it 

£2 



£0 OF THE HUMAN MIND. [CHAP. 1. 

hath produced a system of scepticism, that seems 
to triumph over all science, and even over the 
dictates of common sense. 

All that we know of the body, is owing to 
anatomical dissection and observation, and it must 
be by an anatomy of the mind, that we can dis- 
cover its powers and principles. 



SECT. II. 

The impediments to oar knowledge of the mind. 

But it must be acknowledged, that this kind 
of anatomy is much more difficult than the 
other, and therefore it needs not seem strange, 
that mankind have made less progress in it. To 
attend accurately to the operations of our minds, 
and make them an object of thought, is no easy 
matter even to the contemplative, and to the 
bulk of mankind is next to impossible. 

An anatomist who hath happy opportunities, 
may have access to examine with his own eyes, 
and with equal accuracy, bodies of all different 
ages, sexes, and conditions; so that what is de- 
fective, obscure, or preternatural in one, may be 
discerned clearly, and in its most perfect state, 
in another. But the anatomist of the mind can- 
not have the same advantage. It is his own mind 



SECT. 2.] INTRODUCTION. 21 

only that lie can examine, with any degree of ac- 
curacy and distinctness. This is the only subject 
he can look into. He may, from outward signs 
collect the operations of other minds; but these 
signs are for the most part ambiguous, and must 
be interpreted by what he perceives within him- 
self. 

So that if a philosopher could delineate to us, 
distinctly and methodically, all the operations of 
the thinking principle within him, which no man 
was ever able to do, this would be only the ana- 
tomy of one particular subject; which would be 
both deficient and erroneous, if applied to human 
nature in general. For, a little reflection may 
satisfy us, that the difference of minds is greater 
than that of any other beings which we consider 
as of the same species. 

Of the various powers and faculties we possess, 
there are some which nature seems both to have 
planted and reared, so as to have left nothing to 
human industry. Such are the powers which we 
have in common with the brutes, and which are 
necessary to the preservation of the individual, 
or the continuance of the kind. There are other 
powers, of which nature hath only planted the 
seeds in our minds, but hath left the rearing of 
them to human culture. It is by the proper cul- 
ture of these that we are capable of all those im- 
provements in intellectuals, in taste, and in mo- 
rals, which exalt and dignify human nature; 
while, on the other hand, the neglect or perver- 
sion of them makes its degeneracy and corruption, 



%% OF THE HUMAN MIND. [CHAP. 1. 

The two-legged animal that eats of nature's 
dainties, what his taste or appetite craves, and 
satisfies his thirst at the crystal fountain, who 
propagates his kind as occasion and lust prompt* 
repels injuries, and takes alternate labour and re- 
pose, is, like a tree in the forest, purely of nature's 
growth. But this same savage hath within him 
the seeds of the logician, the man of taste and 
breeding, the orator, the statesman, the man of 
virtue, and the saint; which seeds, though plant- 
ed in his mind by nature, yet, through want of 
culture and exercise, must lie for ever buried, 
and be hardly perceivable by himself or by others. 

The lowest degree of social life will bring to 
light some of those principles which lay hid in 
the savage state: and according to his training, 
and company, and manner of life, some of them, 
either by their native vigour, or by the force of 
culture, will thrive and grow up to great perfec- 
tion ; others will be strangely perverted from 
their natural form; and others checked, or per- 
haps quite eradicated. 

This makes human nature so various and mul- 
tiform in the individuals that partake of it, that, 
in point of morals, and intellectual endowments, 
it fills up all that gap which w r e conceive to be 
between brutes and devils below and the celestial 
orders above; and such a prodigious diversity of 
minds must make it extremely difficult to dis- 
cover the common principles of the species. 

The language of philosophers, with regard to 
the original faculties of the mind, is so adapted 



ECT. 2.] INTRODUCTION. 23 

to the prevailing system, that it cannot fit any 
other ; like a coat that fits the man for whom it 
was made, and shows him to advantage, which 
yet will sit very awkward upon one of a different 
make, although perhaps as handsome and as well 
proportioned. It is hardly possible to make any 
innovation in our philosophy concerning the mind 
and its operations, without using new words and 
phrases, or giving a different meaning to those 
that are received; a liberty which, even when 
necessary, creates prejudice and misconstruc- 
tion, and which must wait the sanction of time 
to authorize it. For, innovations in language, like 
those in religion and government, are alway sus- 
pected and disliked by the many, till use hath 
made them familiar, and prescription hath given 
them a title. 

If the original perceptions and motions of the 
mind were to make their appearance single and 
unmixed, as we first received them from the 
hand of nature, one accustomed to reflection 
would have less difficulty in tracing them; but 
before we are capable of reflection, they are so 
mixed, compounded and decompounded, by ha- 
bits, associations, and abstractions, that it is hard 
to know what they were originally. The mind 
may in this respect be compared to an apothecary 
or a chemist, whose materials indeed are furnish- 
ed by nature; but for the purposes of his art, he 
mixes, compounds, dissolves, evaporates, and su- 
blimes them, till they put on a quite different ap- 
pearance; so that it is very difficult to kbow 



% OF THE HUMAN MIND. [CHAP. 1. 

what they were at first, and much more to bring 
them back to their original and natural form. 
And this work of the mind is not carried on by 
deliberate acts of mature reason, which we 
might recollect, but by means of instincts, habits, 
associations, and other principles, which operate 
before we come to the use of reason; so that it 
is extremely difficult for the mind to return upon 
its own footsteps, and trace back those operations 
which have employed it since it first began to 
think and to act. 

Could we obtain a distinct and full history of 
all that hath passed in the mind of a child, from 
the beginning of life and sensation, till it grows 
up to the use of reason ; how its infant faculties 
began to work, and how they brought forth and 
ripened all the various notions, opinions, and sen- 
timents, which we find in ourselves when we 
come to be capable of reflection ; this would be 
a treasure of natural history, which would proba- 
bly give more light into the human faculties than 
all the systems of philosophers about them since 
the beginning of the world. But it is in vain to 
wish for what nature has not put within the reach 
of our power. Reflection, the only instrument 
by which we can discern the powers of the mind, 
comes too late to observe the progress of nature, 
in raising them from their infancy to perfection. 

It must therefore require great caution, and 
great application of mind, for a man that is grown 
up in all the prejudices of education, fashion, and 
philosophy, to unrivel his notions and opinions* 



SECT. 2.] INTRODUCTION. &5 

till he finds out the simple and original principles 
of his constitution, of which no account can be 
given but the will of our Maker. This may be 
truly called an analysis of the human faculties; 
and till this is performed, it is in vain we expect 
any just system of the mind; that is, an enumera- 
tion of the original powers and laws of our con- 
stitution, and an explication from them of the 
various phenomena of human nature. 

Success, in an inquiry of this kind, it is not in 
human power to command; but perhaps it is pos- 
sible, by caution and humility, to avoid error and 
delusion. The labyrinth may be too intricate, and 
the thread too fine, to be traced through all its 
windings; but if we stop where we can trace it 
no farther, and secure the ground we have gain- 
ed, there is no harm done; a quicker eye may in 
time trace it farther. 

It is genius, and not the want of it, that adul- 
terates philosophy, and fills it with error and false 
theory. A creative imagination disdains the 
mean offices of digging for a foundation, of re- 
moving rubbish, and carrying materials: leaving 
these servile employments to the drudges in 
science, it plans a design, and raises a fabric. 
Invention supplies materials where they are waul- 
ing, and fancy adds colouring, and every befit- 
ting ornament. The work pleases the eye, and 
wants nothing but solidity and a good foundation. 
It seems even to vie with the works of nature: 
till some succeeding architect blows it into rub- 
bish, and builds as goodly a fabric of his own in 



2o of the human mind. [chap. 1. 

its place. Happily for the present age, the 
castle-builders employ themselves more in ro- 
mance than in philosophy. That is undoubtedly 
their province, and in those regions the offspring 
of fancy is legitimate ; but in philosophy it is all 
spurious. 



SECT. III. 



The present state of this part of philosophy. — Of 
Des Cartes, Malebranche, and Locke. 

That our philosophy concerning the mind and 
its faculties, is but in a very low state, may be 
reasonably conjectured, even by those who never 
have narrowly examined it. Are there any prin- 
ciples with regard to the mind, settled with that 
perspicuity and evidence, which attends the prin- 
ciples of mechanics, astronomy, and optics? — 
These are really sciences built upon laws of nature 
which universally obtain. What is discovered in 
them, is no longer matter of dispute: future ages 
may add to it, but till the course of nature be 
changed, what is already established can never 
be overturned. But when we turn our attention 
inward and consider the phenomena of human 
thoughts, opinions, and perceptions, and endea- 
vour to trace them to the general laws and the 



SECT. 3.] INTRODUCTION. 27 

first principles of our constitution, we are imme- 
diately involved in darkness and perplexity. — 
And if common sense, or the principles of edu- 
cation, happen not to be stubborn, it is odds but 
we end in absolute scepticism. 

Des Cartes finding nothing established in this 
part of philosophy, in order to lay the foundation 
of it deep, resolved not to believe his own exist- 
ence till he should be able to give a good rea- 
son for it. He was, perhaps, the first that took 
up such a resolution: but if he could indeed have 
effected his purpose, and really become diffident 
of his existence, his case would have been de- 
plorable, and without any remedy from reason or 
philosophy. A man that disbelieves his own exist- 
ence, is surely as unfit to be reasoned with, as a 
man that believes he is made of glass. There may 
be disorders in the human frame that may produce 
such extravagancies; but they will never be cured 
by reasoning. Des Cartes indeed would make 
us believe, that he got out of this delirium by this 
logical argument, Cogito, ergo sum. But it is 
evident he was in his senses all the time, and 
never seriously doubted his existence. For he 
takes it for granted in this argument, and proves 
nothing at all. I am thinking, says he, therefore 
I am: and is it not as good reasoning to sav, I 
am sleeping, therefore I am? or, I am doing no- 
thing, therefore I am? If a body moves it must 
exist no doubt; but if it is at rest, it must exist 
likewise. 

Perhaps Des Cartes meant not to assume 



IIS 



28 OF THE HUMAN MIND. [CHAP. 1. 

own existence in tins enthymeme, but the exis- 
tence of thought; and to infer from that the ex- 
istence of a mind, or subject of thought. But 
why did he not prove the existence of his 
thought? Consciousness, it may be said, vouches 
that. But who is voucher of consciousness? Can 
any man prove that his consciousness may not 
deceive him? No man can: nor can we give a 
better reason for trusting to it, than that every 
man, while his mind is sound, is determined by 
the constitution of his nature, to give implicit 
belief to it, and to laugh at, or to pity, the man 
who doubts its testimony. And is not every 
man in his wits, as much determined to take his 
existence upon trust as his consciousness? 

The other proposition assumed in this argu- 
ment, That thought cannot be without a mind or 
subject, is liable to the same objection: not that 
it wants evidence; but that its evidence is no 
clearer, nor more immediate, than that of the 
proposition to be proved by it. And taking all 
these propositions together, — I think, — I am con- 
scious, — Every thing that thinks exists, — I ex- 
ist, — would not every sober man form the same 
opinion of the man who seriously doubted any 
one of them? And if he was his friend, would 
he not hope for his cure from physic and good 
regimen, rather than from metaphysic and logic? 

But supposing it proved, that my thought and 
my consciousness must have a subject, and con- 
sequently that I exist, how do I know that all 
that train and succession of thought which I re- 



SECT. 3.] INTRODUCTION. 2$ 

member, belong to one subject, and that the I of 
this moment, is the very individual I of yester- 
day, and of time past? 

Des Cartes did not think proper to start this 
doubt: but Locke has done it; and in or- 
der to resolve it, gravely determines that per- 
sonal identity consists in consciousness; that is, 
if you are conscious that you did such a thing a 
twelvemonth ago, this consciousness makes you 
to be the very person that did it. Now, con- 
sciousness of what is past can signify nothing 
else but the remembrance that I did it. So that 
Locke's principle must be, That identity con- 
sists in remembrance; and consequently a man 
must lose his personal identity with regard to 
every thing he forgets. 

Nor are these the only instances whereby our 
philosophy concerning the mind appears to be 
very fruitful in creating doubts, but very unhap- 
py in resolving them. 

Des Cartes, Malebranciie, and Locke, have 
all employed their genius and skill to prove the 
existence of a material world : and with very bad 
success. Poor untaught mortals believe undoubt- 
edly, that there is a sun, moon and stars; an 
earth, which we inhabit; country, friends, and 
relations, which we enjoy; land, houses, and 
moveables, which we possess. But philosophers, 
pitying the credulity of the vulgar, resolve to 
have no faith but what is founded upon reason. 
They apply to philosophy to furnish them with 
reason for the belief of those things, which all 



SO OF THE HUMAN MIND. [CHAP. 1. 

mankind have believed without being able to 
give any reason for it. And surely one would 
expect, that, in matters of such importance, the 
proof would not be difficult : but it is the most 
difficult thing in the world. For these three 
great men, with the best good will, have not been 
able, from all the treasures of philosophy, to draw 
one argument, that is fit to convince a man that 
can reason, of the existence of any one thing with- 
out him. Admired Philososphy! daughter of light! 
parent of wisdom and knowledge! if thou art 
she! surely thou hast not yet arisen upon the 
human mind, nor blessed us with more of thy 
rays, than are sufficient to shade a "darkness vi- 
sible' ' upon the human faculties, and to disturb 
that repose and security which happier mortals 
enjoy, who never approached thine altar, nor felt 
thine influence! But if indeed thou hast not 
power to dispel those clouds and phantoms which 
thou hast discovered or created, withdraw this 
penurious and malignant ray: I despise Philoso- 
phy, and renounce its guidance: let my soul 
dwell with Common Sense. 



SECT. 4.] INTRODUCTION. 31 

SECT. IV. 

Apology for those philosophers. 

But instead of despising the dawn of light, we 
ought rather to hope for its increase: instead of 
blaming the philosophers I have mentioned, for 
the defects and blemishes of their system, we 
ought rather to honour their memories, as the 
first discoveries of a region in philosophy former- 
ly unknown, and, however lame and imperfect 
the system may be, they have opened the way to 
future discoveries, and are justly entitled to a great 
share in the merit of them. They have removed 
an infinite deal of rust and rubbish, collected in 
the ages of scholastic sophistry, which had ob- 
structed the way. They have put us in the right 
road, that of experience and accurate reflection. 
They have taught us to avoid the snares of am- 
biguous and ill defined words, and have spoken 
and thought upon this subject with a distinctness 
and perspicuity formerly unknown. They have 
made many openings that may lead to the disco- 
very of truths which they did not reach, or to 
the detection of errors in which they were invo- 
luntarily entangled. 

It may be observed, that the defects and blem- 
ishes in the received philosophy concerning the 
mind, which have most exposed it to the con- 
tempt and ridicule of sensible men, have chiefly 



3& OF THE HUMAN MIND. [CHAP. 1, 

been owing to this; — that the votaries of this 
philosophy, from a natural prejudice in her fa- 
vour, have endeavoured to extend her jurisdic- 
tion beyond its just limits, and to call to her bar 
the dictates of Common Sense. But these de- 
cline this jurisdiction; they disdain the trial of 
reasoning, and disown its authority; they neither 
claim its aid, nor dread its attacks. 

In this unequal contest betwixt Common Sense 
and Philosophy, the latter will always come off 
both with dishonour and loss; nor can she ever 
thrive till this rivalship is dropt, these encroach- 
ments given up, and a cordial friendship restored: 
for, in reality, Common Sense holds nothing of 
Philosophy, nor needs her aid. But, on the other 
hand, Philosophy, (if I may be permitted to 
change the metaphor) has no other root but the 
principles of Common Sense; it grows out of 
them and draws its nourishment from them: se- 
vered from this root, its honours wither, its sap 
Is dried up, it dies and rots. 

The philosophers of the last age, whom I have 
mentioned, did not attend to the preserving this 
union and subordination so carefully as the hon- 
our and interest of philosophy required; but 
those of the present have waged open war with 
Common Sense, and hope to make a complete con- 
quest of it by the subtil ties of Philosophy; an at- 
tempt no less audacious and vain than that of 
the giants to dethrone almighty Jove. 



SECT. 5.]] KJTR0DUCTI0N. S3 



SECT. V. 

Of Bishop Berkeley — the Treatise of Human Na* 
ture — and of Scepticism. 

The present age, I apprehend, has not pro- 
duced two more acute or more practised in this 
part of philosophy, than the Bishop of Cloyne, 
and the author of the Treatise of Human Nature. 
The first was no friend to scepticism, but had 
that warm concern for religious and moral prin- 
ciples which became his order: yet the result of 
his inquiry was, a serious conviction, that there 
was no such thing as a material world; nothing in 
nature but spirits and ideas; and that the belief 
of material substances, and of abstract ideas, are 
the chief causes of all our errors in philosophy, 
and of all infidelity and heresy in religion. His 
arguments are founded upon the principles which 
were formerly laid down by Des Cartes, Male- 
branche, and Locke, and which have been very 
generally received. 

And the opinion of the ablest judges seems to 
be, that they neither have been, nor can be con- 
futed; and that he hath proved, by unanswer- 
able arguments, what no man in his senses can 
believe. 

The second proceeds upon the same principles, 
but carries them to their full length; and as the 

c 



34f OF THE HUMAN MIND. [CHAP. 1. 

Bishop undid the whole material world, this au- 
thor, upon the same grounds, undoes the world 
of spirits, and leaves nothing in nature but ideas 
and impressions, without any subject on which 
they may be impressed. 

It seems to be a peculiar strain of humour in 
this author, to set out in his introduction, by pro- 
mising, with a grave face, no less than a complete 
system of the sciences, upon a foundation en- 
tirely new, to wit, that of human nature -, when 
the intention of the whole work is to show, that 
there is neither human nature nor science in the 
world. It may perhaps be unreasonable to com- 
plain of this conduct in an author, who neither 
believes his own existence nor that of his reader; 
and therefore could not mean to disappoint him, 
or to laugh at his credulity. Yet I cannot ima- 
gine, that the author of the Treatise of Human 
Nature is so sceptical as to plead this apology. 
He believed, against his principles, that he should 
be read, and that he should retain his personal 
identity till he reaped the honour and reputa- 
tion justly due to his metaphysical acumen. In- 
deed, he ingeniously acknowledges, that it was 
only in solitude and retirement that he could 
yield any assent to his own philosophy; society, 
like day-light, dispelled the darkness and fogs of 
scepticism, and made him yield to the dominion 
of Common Sense. Nor did I ever hear him 
charged with doing any thing even in solitude, 
that argued such a degree of scepticism as his 
principles maintained. Surely. if his friends ap- 



SECT. 5. J INTRODUCTION. 35 

prehended this, they would have the chanty never 
to leave him alone. 

Pyrrho the Elean, the father of this philoso- 
phy, seems to have carried it to greater perfec- 
tion than any of his successors: for if we may 
believe Antigonus the Carystian, quoted by Di- 
ogenes Laertius, his life corresponds to his 
doctrine. And therefore, if a cart run against 
him, or a dog attacked him, or if he came upon 
a precipice, he would not stir a foot to avoid the 
danger, giving no credit to his senses. But his 
attendants, who, happily for him, were not so 
great sceptics, took care to keep him out of 
harm's way; so that he lived till he was ninety 
years of age. Nor is it to be doubted, but this 
author's friends would have been equally careful 
to keep him from harm, if ever his principles had 
taken too strong a hold of him. 

It is probable the Treatise of Human Nature 
was not written in company; yet it contains 
manifest indications, that the author every now 
and then relapsed into the faith of the vulgar, 
and could hardly, for half a dozen pages, keep 
up the sceptical character. 

In like manner, the great Pyrrho himself, for- 
got his principles on some occasions; and is said 
once to have been in such a passion with his 
cook, who probably had not roasted his dinner to 
his mind, that with the spit in his hand, and the 
meat upon it, he pursued him even into the 
market-place. 

It is a bold philosophy that rejects, without 



86 OF THE HUMAN MIND. [CHAP. 1. 

ceremony, principles which irresistibly govern 
the belief and the conduct of all mankind in the 
common concerns of life; and to which the phi- 
losopher himself must yield, after he imagines he 
hath confuted them. Such principles are older, 
and of more authority, than Philosophy: she 
rests upon them as her basis, not they upon her. 
If she could overturn them, she must be buried 
in their ruins; but all the engines of philosophi- 
cal subtilty are too weak for this purpose; and 
the attempt is no less ridiculous than if a me- 
chanic should contrive an axis in peritrochio to 
remove the earth out of its place; or if a mathe- 
matician should pretend to demonstrate, that 
things equal to the same thing are not equal to 
one another. 

Zeno endeavoured to demonstrate the impossi- 
bility of motion ; Hobbes, that there was no dif- 
ference between right and wrong; and this au- 
thor, that no credit is to be given to our senses, 
to our memory, or even to demonstration. Such 
philosophy is justly ridiculous, even to those who 
cannot detect the fallacy of it. It can have no 
other tendency, than to shew the acuteness of the 
sophist, at the expence of disgracing reason and 
human nature, and making mankind Yahoos. 



SECT. 6.] INTRODUCTION. Sf 

SECT. VI. 

Of the Treatise of Human Nature. 

There are other prejudices against this system 
of human nature, which, even upon a general 
view, may make one diffident of it. 

Des Cartes, Hobbes, and this author, have 
each of them given us a system of human nature; 
an undertaking too vast for any one man, how 
great soever his genius and abilities may be. 
There must surely be reason to apprehend, that 
many parts of human nature never came under 
their observation; and that others have been 
stretched and distorted, to fill up blanks, and 
complete the system. Christopher Columbus, 
or Sebastian Cabot, might almost as reasonably 
have undertaken to give us a complete map of 
America. 

There is a certain character and style in Na- 
ture's works, which is never attained in the most 
perfect imitation of them. This seems to be 
wanting in the systems of human nature I have 
mentioned, and particularly in the last. One 
may see a puppet make variety of motions and 
gesticulations, which strike much at first view; 
but when it is accurately observed, and taken to 
pieces, our admiration ceases; we comprehend 
the whole art of the maker. How unlike is it to 
that which it represents! what a poor piece of 

c 3 



38 OF THE HUMAN MIND. [CHAP. I, 

work compared with the body of a man, whose 
structure the more we know, the more wonders 
we discover in it, and the more sensible we are 
of our ignorance! Is the mechanism of the mind 
so easily comprehended, when that of the body 
is so difficult? Yet, by this system, three laws 
of association, joined to a few general feelings, ex- 
plain the whole mechanism of sense, imagination, 
memory, belief, and of all the actions and passions 
of the mind. Is this the man that nature made? 
I suspect it is not so easy to look behind the 
scenes in Nature's work. This is a puppet sure- 
ly, contrived by too bold an apprentice of Na- 
ture, to mimic her work. It shews tolerably by 
candle-light, but brought into clear day, and 
taken to pieces, it will appear to be a man made 
with mortar and trowel. The more we know of 
other parts of nature, the more we like and ap- 
prove them. The little I know of the planetary 
system; of the earth which we inhabit of min- 
erals, vegetables, and animals; of my own body, 
and of the law 7 s which obtain in these parts of 
nature; opens to my mind grand and beautiful 
scenes, and contributes equally to my happiness 
and power. But when I look within, and con- 
sider the Mind itself, which makes me capable 
of all these prospects and enjoyments; if it is in- 
deed what the Treatise of Human Nature makes 
it, I rind I have been only in an enchanted castle, 
imposed upon by spectres and apparitions. I blush 
inwardly to think how I have been deluded; I 
am ashamed of my frame; and can hardly forbear 



SECT. 7-] INTRODUCTION. 3§ 

expostulating with my destiny: Is this thy pas- 
time, O Nature, to put such tricks upon a silly 
creature, and then to take off the mask, and shew 
him how he hath been befooled? If this is 
the philosophy of human nature, my soul enter 
thou not into her secrets. It is surely the for- 
bidden tree of knowledge ; I no sooner taste of 
it, than I perceive myself naked, and stript of 
all things, yea, even of my very self. I see my- 
self, and the whole frame of Nature, shrink intOj 
fleeting ideas, which, like Epicurus's atoms 3 
dance about in emptiness. 



SECT. VII, 



The system of all these authors is the same, and leads 
to scepticism. 

But what if these profound disquisitions into 
the first principles of human nature, do naturally 
and necessarily plunge a man into this abyss of 
scepticism? May we not reasonably judge from 
what hath happened? Des Cartes no sooner be- 
gan to dig in this mine, than scepticism was rea- 
dy to break in upon him. He did what he could 
to shut it out. Malebranche and Locke, who 
dug deeper, found the difficulty of keeping out 
this enemy still to increase 5 but they laboured 



40 OF THE HUMAN MIND. [CHAP. 1. 

honestly in the design. Then Berkeley, who 
carried on the work, despairing of securing all, 
bethought himself of an expedient: By giving 
up the material world, which he thought might 
be spared without loss, and even with advantage, 
he hoped, by an impregnable partition, to secure 
the world of spirits. But, alas! the Treatise of 
Human Nature wantonly sapped the foundation 
of this partition, and drowned all in one univer- 
sal deluge. 

These facts, which are undeniable, do indeed 
give reason to apprehend, that Des Cartes's 
system of the human understanding, which I 
shall beg leave to call the ideal system, and which 
with some improvements made by later writers, 
is now generally received, hath some original 
defect; that this scepticism is inlaid in it, and 
reared along with it; and, therefore, that we 
must lay it open to the foundation, and examine 
the materials, before we can expect to raise any 
solid and useful fabric of knowledge on this sub- 
ject. 



SECT. 8.] INTRODUCTION. 41 

SECT. VIII. 

We ought not to despair of a better. 

But is this to be despaired of, because Des 
Cartes and his followers have failed ? By no 
means. This pusillanimity would be injurious to 
ourselves, and injurious to truth. Useful discove- 
ries are sometimes indeed the effect of superior 
genius, but more frequently they are the birth of 
time and of accidents. A traveller of good judg- 
ment may mistake his way, and be unawares led 
into a wrong track; and when the road is fair 
before him, he may go on without suspicion, and 
be followed by others; but when it ends in a 
coal-pit, it requires no great judgment to know 
that he hath gone wrong, nor perhaps to rind out 
what misled him. 

In the mean time, the unprosperous state of 
this part of philosophy had produced an effect, 
somewhat discouraging indeed to any attempt of 
this nature, but an effect which might be expect- 
ed, and which time only and better success can re- 
medy. Sensible men, w 7 ho never will be sceptics 
in matters of common life, are apt to treat with 
sovereign contempt every thing that hath been 
said, or is to be said, upon this subject. — It is 
metaphysic, say they: Who minds it? Let 
scholastic sophisters entangle themselves in their 
own cobwebs; I am resolved to take my own 



42 OF THE HUMAN MIND. [CHAP. 1. 

existence, and the existence of other things, upon 
trust; and to believe that snow is cold, and 
honey sweet, whatever they may say to the con- 
trary. He must either be a fool, or want to 
make a fool of me, that would reason me out of 
my reason and senses. 

I confess I know not what a sceptic can an- 
swer to this, nor by what good argument he can 
plead even for a hearing; for either his reason- 
ing is sophistry, and so deserves contempt; or 
there is no truth in the human faculties, and then 
why should we reason? 

If therefore aman find himself entangled in these 
metaphysical toils, and can find no other way to 
escape, let him bravely cut the knot which he 
cannot loose, curse metaphysic, and dissuade 
every man from meddling with it. For if I have 
been led into bogs and quagmires, by following 
an ignis Jatnus, what can I do better, than to 
warn others to beware of it? If Philosophy con- 
tradicts herself, befools her votaries, and deprives 
them of every object worthy to be pursued or 
enjoyed, let her be sent back to the infernal re- 
gions from which she must have had her ori- 
ginal. 

But is it absolutely certain that this fair lady 
is of the party? Is it not possible she may have 
been misrepresented? Have not men of genius 
in former ages often made their own dreams to 
pass for her oracles? Ought she then to be con- 
demned without any further hearing? This 
would be unreasonable. I have found her in all 



SECT. 8. INTRODUCTION. 43 

other matters an agreeable companion, a faithful 
counsellor, a friend to Common Sense, and to 
the happiness of mankind. This justly entitles 
her to my correspondence and confidence, till I 
find infallible proofs of her infidelity. 



44 OF THE HUMAN MIND. £ CHAP. 2. 



CHAP. IL 



OF SMELLING. 



SECT. I. 

.The order of proceeding. Of the medium and 
organ of Smell. 

It is so difficult to unravel the operations of the 
human understanding, and to reduce them to 
their first principles, that we cannot expect to 
succeed in the 'attempt, but by beginning with 
the simplest, and proceeding by very cautious 
steps to the more complex. The five external 
senses may, for this reason, claim to be first con- 
sidered in an analysis of the human faculties. 
And the same reason ought to determine us to 
make a choice even among the senses, and to 
give the precedence, not to the noblest, or most 
useful, but to the simplest, and that whose ob- 
jects are least in danger of being mistaken for 
other things. 

In this view, an analysis of our sensations may 
be carried on, perhaps with most ease and dis- 
tinctness, by taking them in this order: Smell- 
ing, Tasting, Hearing, Touch, and, last of all, 
Seeing. 



SECT. 1.] INTRODUCTION. 45 

Natural philosophy informs us, that all animal 
and vegetable bodies, and probably all or most 
other bodies, while exposed to the air, are con- 
tinually sending forth effluvia of vast subtilty, 
not only in their state of life and growth, but in 
the states of fermentation and putrefaction: 
These volatile particles do probably repel each 
other, and so scatter themselves in the air, until 
they meet with other bodies to which they have 
some chemical affinity, and with which they 
unite, and form new concretes. All the smell of 
plants, and of other bodies, is caused by these 
volatile parts, and is smelled wherever they are 
scattered in the air: And the acuteness of 
smell in some animals, shew us, that these ef- 
fluvia spread far, and must be inconceivably sub- 
tile. 

Whether, as some chemists conceive, every 
species of bodies hath a spiritus rectus, a kind of 
soul, which causes the smell, and all the specific 
virtues of that body, and which being extremely 
volatile, flies about in the air in quest of a proper 
receptacle, I do not inquire. This, like most 
other theories, is perhaps rather the product of 
imagination than of just induction. But that all 
bodies are smelled by means of effluvia which 
they emit, and which are drawn into the nostrils 
along with the air, there is no reason to doubt. 
So that there is manifest appearance of design in 
placing the organ of smell in the inside of that, 
canal, through which the air is continually passing 
in inspiration and expiration. 



46 OF THE HUMAN MIND. [CHAP. &* 

Anatomy informs us, that the membrana pitui- 
tariu, and the olfactory nerves, which are distri- 
buted to the villous parts of this membrane, are 
the organs destined by the wisdom of nature to 
this sense ; so that when a body emits no effluvia, 
or when they do not enter into the nose, or when 
the pituitary membrane or olfactory nerves are 
rendered unfit to perform their office, it cannot 
be smelled. 

Yet, notwithstanding this, it is evident that 
neither the organ of smell, nor the medium, nor 
any motions we can conceive excited in the 
membrane above-mentioned, or in the nerve or 
animal spirits, do in the least resemble the sensa- 
tion of smelling; nor could that sensation of it- 
self ever have led us to think of nerves, animal 
spirits, or effluvia. 



SECT. II. 

The sensation considered abstractly. 

Having premised these things, with regard to 
the medium and organ of this sense, let us now 
attend carefully to what the mind is conscious of 
when we smell a rose or a lily; and since our 
language affords no other name for this sensa- 
tion, we shall call it a smell or odour, carefully 



SECT. 2.] .INTRODUCTION. 47 

excluding from the meaning of those names every 
thing but the sensation itself, at least till we have 
examined it. 

Suppose a person who never had this sense be- 
fore, to receive all at once, and to smell a rose; 
can he perceive any similitude or agreement be- 
tween the smell and the rose? or indeed between 
it and any other object whatsoever? Certainly 
he cannot. He finds himself affected in a new 
way, he knows not why or from what cause. 
Like a man that feels some pain or pleasure for- 
merly unknown to him, he is conscious that he is 
not the cause of it himself; but cannot from the 
nature of the thing, determine whether it is caus- 
ed by body or spirit, by something near, or by 
something at a distance. It has no similitude to 
any thing else, so as to admit of a comparison; 
and therefore he can conclude nothing from it, 
unless perhaps that there must be some unknown 
cause of it. 

It is evidently ridiculous, to ascribe to it figure, 
colour, extension, or any other quality of bodies. 
He cannot give it a place, any more than he can 
give a place to melancholy or joy: nor can he 
conceive it to have any existence but when it is 
smelled. So that it appears to be a simple and 
original affection or feeling of the mind, alto- 
gether inexplicable and unaccountable. It is in- 
deed impossible that it can be any body : It is a 
sensation ; and a sensation can only be in a sen- 
tient thing. 

The various odours have each their different 



48 OF THE HUMAN MIND.- [CHAP. 2. 

degrees of strength or weakness. Most of them 
are agreeable or disagreeable; and frequently 
those that are agreeable when weak, are disa- 
greeable when stronger. When we compare 
different smells together, we can perceive very 
few resemblances or contrarieties, or indeed re- 
lations of any kind between them* They are all 
so simple in themselves, and so different from 
each other, that it is hardly possible to divide 
them into genera and species. Most of the names 
we give them are particular; as the smell of a 
rose, of a jessamine, and the like. Yet there are 
some general names; as sweet, stinking, musty, 
putrid, cadaverous^ aromatic. Some of them seem 
to refresh and animate the mind, others to deaden 
and depress it. 



SECT. III. 



Sensation and remembrance, natural principles of 
belief. 

So far we have considered this sensation abstract- 
ly. Let us next compare it with other things to 
which it bears some relation. And first I shall 
compare this sensation with the remembrance 
and the imagination of it. 

I can think of the smell of a rose when I do 



SECT. 3.] OF SMELLING, 4Q 

not smell it; and it is possible that when I think 
of it, there is neither rose nor smell any where 
existing. But w r hen I smell it, I am necessarily 
determined to believe that the sensation really 
exists. This is common, to all sensations, that 
as they cannot exist but in being perceived; so 
they cannot be perceived,, but they must exist* 
I could as easily doubt of my own existence, as. 
of the existence of my sensations. Even those 
profound philosophers who have endeavoured to- 
disprove their own existence, have yet left their 
sensation sto stand upon their own bottom, stript 
of a subject, rather than call in question the 
reallity of their existence. 

Here then a sensation, a smell for instance, 
may be presented to the mind three different 
ways: It maybe smelled, it maybe remembered, 
it may be imagined or thought of. In the first 
case, it is necessarily accompanied with a belief 
of its present existence; in the second, it is ne- 
cessarily accompanied with a belief of its past 
existence; and in the last, it is not accompanied 
with belief at all, but is what the logicians call a 
simple apprehension. 

Why sensation should compel our belief of the 
present existence of the thing, memory a belief 
of its past existence, and imagination no belief 
at all, I believe no philosopher can give a shadow 
of reason, but that such is the nature of these 
operations: They are all simple and original, and 
therefore inexplicable acts of the mind. 

Suppose that once, and only once, I smelled a 

D 



50 OF THE HUMAN MIND. [CHAP. 2. 

tuberose in a certain room where it grew in a 
pot, and gave a very grateful perfume. Next 
clay I relate what I saw and smelled. When I 
attend as carefully as I can tq what passes in my 
mind in this case, it appears evident, that the 
very thing I saw yesterday, and the fragrance I 
smell ed, are now the immediate objects of my 
mind when I remember it. Further, I can ima- 
gine this pot and flower transported to the room 
where I now sit, and yielding the same perfume. 
Here likewise it appears, that the individual 
thing which I saw and smelled, is the object of 
my imagination. 

Philosophers indeed tell me, that the imme- 
diate object of my memory and imagination in 
this case, is not the past sensation, but an idea 
of it, an image, phantasm, or species of the odour 
I smelled: that this idea now exists in my mind, 
or in my sensorium; and the mind contemplating 
this present idea, finds it a representation of what 
is past, or of what may exist; and accordingly 
calls it memory or imagination. This is the 
doctrine of the ideal philosophy; which we shall 
not now examine, that we may not interrupt the 
thread of the present investigation. Upon the 
strictest attention, memory appears to me to 
have things that are past, and not present ideas, 
for its object. We shall afterwards examine 
this system of ideas, and endeavour to make it 
appear, that no solid proof has ever been ad- 
vanced of the existence of ideas; that they are 
a mere fiction and hypothesis, contrived to solve 



SECT. 3.] OF SMELLING. 51 

the phenomena of the human understanding; 
that they do not at all answer this end; and that 
this hypothesis of ideas or images of things in the 
mind, or in the sensorium, is the parent of those 
many paradoxes so shocking to common sense, 
and of that scepticism, which disgrace our phi- 
losophy of the mind, and have brought upon it 
the ridicule and contempt of sensible men. 

In the mean time, I beg leave to think with 
the vulgar, that when I remember the smell of 
the tuberose, that very sensation which I had 
yesterday, and which has now no more any exis- 
tence, is the immediate object of my memory; 
and when I imagine it present, the sensation it- 
self, and not any idea of it, is the object of my 
imagination. But though the object of my sen- 
sation, memory, and imagination,, be in this case 
the same, yet these acts or operations of the mind 
are as different, and as easily distinguishable, . as 
smell, taste, and sound. I am conscious, of" a 
difference in kind between sensation and memory, 
and between both and imagination. I find this 
also, that the sensation compels my belief of the 
present existence of the smell, and memory my 
belief of its- past existence. There is a smell, is 
the immediate testimony of sense;, there was a 
smell, is the immediate testimony of memory. 
If you ask me, why I believe that the smell ex- 
ists? I can give no other reason, nor shall ever 
be able to give any other, than that I smell it. 
If you ask, why I believe that it existed yester- 
day? I can give no other reason but that I re- 
member it, d 2 



D 






52 OF THE HUMAN MIND. [CHAP. 2. 

Sensation and memory therefore are simple, 
original, and perfectly distinct operations of the 
mind, and both of them are original principles of 
belief. Imagination is distinct from both, but is 
no principle of belief. Sensation implies the pre- 
sent existence of its object; memory its past 
existence; but imagination views its object na- 
ked, and without any belief of its existence or 
non-existence, and is therefore what the schools 
call simple apprehension. 



SECT. IV. 



Judgment and belief in some cases precede simple 
apprehension. 

But here again the ideal system comes in our 
way; it teaches us, that the first operation of the 
mind about its ideas, is simple apprehension; 
that is, the bare conception of a thing without 
any belief about it; and that after we have got 
simple apprehensions, by comparing them toge- 
ther, we perceive agreements or disagreements 
between them; and that this perception of the 
agreement or disagreement of ideas, is all that 
we call belief, judgment or knowledge. Now this 
appears to me to be all fiction, without any foun- 
dation in nature: for it is acknowledged by all, 
that sensation must go before memory and ima- 
gination ; and hence it necessarily follows, that 
apprehension accompanied with belief and know. 



SECT. 4.] OF SMELLING. 53 

ledge, must go before simple apprehension, at 
least in the matters we are now speaking of. 
So that here, instead of saying, that the belief or 
knowledge is got by putting together and com- 
paring the simple apprehensions, we ought rather 
to say, that the simple apprehensions is performed 
by resolving and analysing a natural and original 
judgment. And it is with the operations of the 
mind, in this case, as with natural bodies, which 
are indeed compounded of simple principles or 
elements. Nature does not exhibit these ele- 
ments separate, to be compounded by us; she 
exhibits them mixed and compounded in concrete 
bodies, and it is only by art and chemical analy- 
sis that they can be separated. 



SECT. V. 



Two theories of the nature of belief refuted* Con~ 
elusions from what hath been said. 

But what is this belief or knowledge which ac- 
companies sensation and memory? Every man 
knows what it is, but no man can define it. Does 
any man pretend to define sensation, or to define 
consciousness? It is happy indeed that no man 
does. And if no philosopher had attempted to 
define and explain belief, some paradoxes in phi- 
losophy, more incredible than ever were brought 
forth by the most abject superstition, or the most 

d3 



•?1 J OF THE HUMAN MIND. [CHAP. 2. 

frantic enthusiasm, had never seen the light. Of 
this kind surely is that modern discovery of the 
ideal philosophy, that sensation, memory, belief 
and imagination, when they have the same object, 
are only different degrees of strength and vivacity 
in the idea. Suppose the idea to be that of a 
future state after death; one man believes it 
firmly ; this means no more than that he hath a 
strong and lively idea of it: Another neither 
believes nor disbelieves; that is, he has a weak 
and faint idea. Suppose now a third person be- 
lieves firmly that there is no such thing; I am 
at a loss to know whether his idea be faint or 
lively: If it is faint, then there may be a firm 
belief, where the idea is faint; if the idea is 
lively, then the belief of a future state and the 
belief of no future state must be one and the 
same. The same arguments that are used to 
prove that belief implies only a stronger idea of 
the object than simple apprehension, might as 
well be used to prove that love implies only a 
stronger idea of the object than indifference. 
And then what shall we say of hatred, which must 
upon this hypothesis be a degree of love, or a de- 
gree of indifference? If it should be said, that 
in love there is something more than an idea, to 
wit, an affection of the mind; may it not be said 
with equal reason, that in belief there is some- 
thing more tlian an idea, to wit, an assent or per- 
suasion of the mind. 

But perhaps it may be thought as ridiculous to 
argue against this strange opinion, as to maintain 



SECT. 5.] OF SMELLING. 55 

it. Indeed, if a man should maintain, that a circle, 
a square, and a triangle, differ only in magnitude, 
and not in figure, I believe he would find nobody 
disposed either to believe him or argue against 
him; and yet I do not think it less shocking to 
common sense, to maintain, that sensation, me- 
mory, and imagination, differ only in degree, and 
not in kind. I know it is said, that in a delirium 
or in dreaming, men are apt to mistake one for 
the other. But does it follow from this, that men 
who are neither dreaming nor in a delirium, can- 
not distinguish them ? But how does a man 
know, that he is not in a delirium? I cannot 
tell. Neither can I tell how a man knows that 
he exists: But if any man seriously doubts whe- 
ther he is in a delirium, I think it highly proba- 
ble that he is, and that it is time to seek for a cure, 
which I am persuaded he will not find in the 
whole system of logic. 

I mentioned before Locke's notion of belief or 
knowledge : he holds that it consists in a percep- 
tion of the agreement or disagreement of ideas; 
and this he values himself upon as a very impor- 
tant discovery. 

We shall have occasion afterwards to examine 
more particularly this grand principle of Locke's 
philosophy, and to shew that it is one of the main 
pillars of modern scepticism, although he had no 
intention to make that use of it. At present let 
us only consider how it agrees with the instances 
of belief now under consideration; and whether 
it gives any light to' them. I believe that the 



50 O* THE HUMAN MIND. £CHAP. 2. 

sensation I have exists; and that the sensation I 
remember, does not now exist, but did exist yes- 
terday. Here, according to Locke's system, I 
compare the idea of a sensation with the ideas of 
past and present existence: at one time that 
this idea agrees with that of present existence, 
but disagrees with that of past existence; but 
at another time it agrees with the idea of past 
existence, and disagrees with that of present ex- 
istence. Truly these ideas seem to be very capri- 
cious in their agreements and disagreements. — 
Besides, I cannot for my heart conceive what is 
meant by either. I say a sensation exists, and I 
think I understand clearly what I mean. But you 
want to make the thing clearer, and for that end 
tell me, that there is an agreement between the 
idea of that sensation and the idea of existence. 
To speak freely, this conveys to me no light, but 
darkness; I can conceive no otherwise of it, than 
as an odd and obscure circumlocution. I con- 
clude, then, that the belief which accompanies 
sensation and memory, is a simple act of the 
mind, which cannot be defined. It is in this re- 
spect like seeing and hearing, which can never 
be so defined as to be understood by those who 
have not these faculties : and to such as have 
them, no definition can make these operations 
more clear than they are already. In like 
manner, every man that has any belief, and he 
must be a curiosity that has none, knows per- 
fectly what belief is, but can never define nor 
explain it. I conclude also, that sensation^ me- 



SECT. 5.] OF SMELLING. 57 

mory, and imagination, even where they have the 
same objects, are operations of a quite different 
nature, and perfectly distinguishable by those 
who are sound and sober. A man that is in dan- 
ger of confounding them, is indeed to be pitied; 
but whatever relief he may find from another art, 
he can find none from logic or metaphysic. I 
conclude farther, that it is no less a part of the 
human constitution, to believe the present exist- 
ence of our sensations, and to believe the past 
existence of what we remember, that it is to be- 
lieve that twice two make four. The evidence 
of sense, the evidence of memory, and the evi- 
dence of the necessary relations of things, are all 
distinct and original kinds of evidence, equally 
grounded on our constitution: none of them de- 
pends upon, or can be resolved into another. 
To reason against any of these kinds of evidence, 
is absurd; nay, to reason for them, is absurd. 
They are first principles; and such fall not with- 
in the province of Reason, but of Common 
Sense. 



SECT. VI. 



Apology for metaphysical absurdities. Sensation 
without a sentient, a consequence of the theory of 
ideas. Consequences of this strange opinion. 

Having considered the relation which the sen- 
sation of smelling bears to the remembrance and 



58 OF THE HUMAN MIND. [CHAP. 2. 

imagination of it, I proceed to consider, what 
relation it bears to a mind or sentient principle. 
It is certain, no man can conceive or believe 
smelling to exist of itself, without a mind, or 
something that has the power of smelling, of 
which it is called a sensation, an operation, or 
feeling. Yet if any man should demand a proof, 
that sensation cannot be without a mind or sen- 
tient being, I confess that 1 can give none; and 
that to pretend to prove it, seems to be almost as 
absurd as to deny it. 

This might have been said without any apology 
before the Treatise of Human Nature appeared 
in the world. For till that time, no man, as far 
as I know, ever thought either of calling in ques- 
tion that principle, or of giving a reason for his 
belief of it. Whether thinking beings were of an 
ethereal or igneous nature, whether material or 
immaterial, was variously disputed; but that 
thinking is an operation of some kind of being or 
other, was always taken for granted, as a princi- 
ple that could not possibly admit of doubt. 

However, since the author above-mentioned, 
who is undoubtedly one of the most acute meta- 
physicians that this or any age hath produced, 
hath treated it as a vulgar prejudice, and main- 
tained, that the mind is only a succession of 
ideas and impressions without any subject; his 
opinion, however contrary to the common appre- 
hensions of mankind, deserves respect. I beg, 
therefore, once for all, that no offence may be 
taken at charging this or other metaphysical no- 



SECT. 6.] OF SMELLING. 59 

tions with absurdity, or with being contrary to 
the common sense of mankind. No disparage- 
ment is meant to the understandings of the au- 
thors or maintainers of such opinions. Indeed, 
they commonly proceed not from defect of un- 
derstanding, but from an excess of refinement: 
the reasoning that leads to them, often gives 
new light to the subject, and shows real genius 
and deep penetration in the author; and the pre- 
mises do more that atone for the conclusion. 

If there are certain principles, as I think there 
are, which the constitution of our nature leads us 
to believe, and which we are under a necessity to 
take for granted in the common concerns of life, 
without being able to give a reason for them; 
these are what we call the principles of common, 
sense; and what is manifestly contrary to them, 
is what we call absurd. 

Indeed if it is true, and to be received as a prin- 
ciple of philosophy, That sensation and thought 
may be without a thinking being; it must be ac- 
knowledged to be the most wonderful discovery 
that this or any other age hath produced. The 
received doctrine of ideas is the principle from 
which it is deduced, and of which indeed it seems 
to be a just and natural consequence. And it is 
probable, that it would not have been so late a 
discovery, but that it is so shocking and repug- 
nant to the common apprehensions of mankind, 
that it required an uncommon degree of philoso- 
phical intrepidity to usher it into the world. It is 
a fundamental principle of the ideal system, That 
every object of thought must be an impression, 



60 OF THE HUMAN MIND. [CHAP, g. 

or an idea, that is, a faint copy of some preceding 
impression. This is a principle so commonly re- 
ceived, that the author above-mentioned, although 
his whole system is built upon it, never offers the 
least proof of it. It is upon this principle, as a 
fixed point, that he erects his metaphysical en- 
gines, to overturn heaven and earth, body and 
spirit. And indeed, in my apprehension, it is 
altogether sufficient for the purpose. For if im- 
pressions and ideas are the only objects of thought, 
then heaven aud earth, and body and spirit, and 
every thing you please, must signify only impres- 
sions and ideas, or they must be words without 
any meaning. It seems, therefore, that this no- 
tion, however strange, is closely connected with 
the received doctrine of ideas, and we must ei- 
ther admit the conclusion, or call in question the 
premises. 

Ideas seem to have something in their nature 
unfriendly to other existences. They were first 
introduced into philosophy, in the humble cha- 
racter of images or representatives of things; 
and in this character they seemed not only to be 
inoffensive, but to serve admirably well for ex- 
plaining the operations of the human understand- 
ing. But since men began to reason clearly and 
distinctly about them, they have by degrees sup- 
planted their constituents, and undermined the 
existence of every thing but themselves. First, 
they discarded all secondary qualities of bodies ; 
and it was found out by their means, that fire is 
not hot, nor snow cold, nor honey sweet; and in 
a wi/rd, that heat and cold, sound, colour, taste, 



SECT. 6.] OF SMELLING. 61 

and smell, are nothing but ideas or impressions. 
Bishop Berkeley advanced them a step higher, 
and found out by just reasoning, from the same 
principles, that extension, solidity, space, figure, 
and body, are ideas, and that there is nothing in 
nature but ideas and spirits. But the triumph of 
ideas was completed by the Treatise of Human 
Nature, which discards spirits also, and leaves 
ideas arid impressions as the sole existences in the 
universe. What if at last, having nothing else to 
contend with, they should fall foul of one 
another, and leave no existence in nature at all? 
This would surely bring philosophy into danger; 
for what should we have left to talk or to dispute 
about? 

However, hitherto these philosophers acknow- 
ledge the existence of impressions and ideas; 
they acknowledge certain laws of attraction, or 
rules of precedence, according to which ideas 
and impressions range themselves in various 
forms, and succeed one another: but that they 
should belong to a mind, as its proper goods and 
chattels, this they have found to be a vulgar er- 
ror. These ideas are as free and independent as 
the birds of the air, or as Encunus's atoms when 
they pursued their journey in the vast inane. 
Shall we conceive them like the films of things in 
the Epicurean system. 

Princijrio hoc dico, rerum simulacra vagari, 

Mvlta modis multis, in cunctas undique parlcis 

Yenvia, oi«t facile inter se junguntur in auris, 

Obvia cum veniunt. Luca. 



62 OF THE HUMAN MIND, [CHAP. 2. 

Or do they rather resemble Aristotle's intelli- 
gible species after they are shot forth from the 
object, and before they have yet struck upon the 
passive intellect? But why should we seek to 
compare them with any thing, since there is no- 
thing in nature but themselves? They make the 
whole furniture of the universe ; starting into ex- 
istence, or out of it, without any cause; combin- 
ing into parcels, which the vulgar call minds; and 
succeeding one another by fixed laws, without 
time, place, or author of those laws. 

Yet, after all, these self-existent and inde- 
pendent ideas look pitifully naked and destitute, 
when left thus alone in the universe, and seem 
upon the whole, to be in a worse condition than 
they were before. Des Cartes, Malebranche, 
and Lock, as they made much use of ideas, 
treated them handsomely, and provided them in 
decent accommodation; lodging them either in 
the pineal gland, or in the pure intellect, or even 
in the divine mind. They moreover clothed 
them with a commission, and made them repre- 
sentatives of things, which gave them some digni- 
ty and character. But the Treatise of Human Na- 
ture, though no less indebted to them, seems to have 
made but a bad return, by bestowing upon them 
this independent existence; since thereby they 
are turned out of house and home, and set adrift 
in the world, without friend or connection, 
without a rag to cover their nakedness ; and who 
knows but the whole system of ideas may perish by 
the indiscreet zeal of their friends to exalt them? 



SECT. 6.] OF SMELLING. 63 

However this may be, it is certainly a most 
amazing discovery, that- thought and ideas may 
be without any thinking being: — a discovery big 
with consequences which cannot be easily traced 
by those deluded mortals who think and reason 
in the common track. We were always apt to 
imagine, that thought supposed a thinker, and 
love a lover, and treason a traitor: but this, it 
seems, was all a mistake; and it is found out, 
that there may be treason without a traitor, and 
love without a lover, laws without a legislator, 
and punishment without a sufferer, succession 
without time, and motion without any thing 
moved, or space in which it may move: or if, 
in these cases, ideas are the lover, the sufferer, 
the traitor, it were to be wished that the author 
of this discovery had further condescended to 
acquaint us, whether ideas can converse together, 
and be under obligations of duty or gratitude to 
each other; whether they can make promises, 
and enter into leagues and covenants, and fulfil 
or break them, and be punished for the breach? 
If one set of ideas makes a covenant, another 
breaks it, and a third is punished for it, there is 
reason to think that justice is no natural virtue 
in this system. 

It seemed very natural to think, that the Trea- 
tise of Human Nature required an Author, and a 
very ingenious one too; but now we learn, that 
it i« only a set of ideas that came together, and 
arranged themselves by certain associations and 
attractions. 

After all, this curious system appears not to 



64 OF THE HUMAN MIND. [CHAP. 2. 

be fitted to the present state of human nature. 
How far it may suit some choice spirits, who are 
refined from the drags of common sense, I cannot 
say. It is acknowledged, I think, that even 
these can enter into this system only in their 
most speculative hours, when they soar ^o high 
in pursuit of those self-existent ideas, as to lose 
sight of all other things. But when they con- 
descend to mingle again with the human race, 
and to converse with a friend, a companion, or a 
fellow citizen, the ideal system vanishes; com- 
mon sense, like an irresistible torrent, carries 
them along; and, in spite of all their reasoning 
and philosophy, they believe their own existence, 
and the existence of other things. 

Indeed, it is happy they do so; for if they should 
carry their closet belief into the world, the rest 
of mankind would consider them as diseased, 
and send them to an infirmary. Therefore as 
Plato required certain previous qualifications of 
those who entered his school, I think it would 
be prudent for the doctors of this ideal philoso- 
phy to do the same, and to refuse admittance to 
every man who is so weak, as to imagine that he 
ought to have the same belief in solitude and in 
company, or that his principles ought to have 
any influence upon his practice : for this philoso- 
phy is like a hobby-horse, which a man in bad 
health may ride in his closet, without hurting his 
reputation ; but if he should take him abroad with 
him to church, or to the exchange, or to the 
play-house, his heir would imediately call a jury 
and seize his estate. 



SECT. 70 0P SMELLING. 65 



SECT. VII. 

The conception and belief of a sentient being or 
mind, is suggested by our constitution. The 
notion of relations not always got by comparing 
the related ideas. 

Leaving this philosophy, therefore, to those 
who have occasion for it, and can use it discreet- 
ly as a chamber exercise, we may still inquire, 
how the rest of mankind, and even the adepts 
themselves, except in some solitary moments, 
have got so strong and irresistible a belief^ that 
thought must have a subject, and be the act of 
some thinking being: how every man believes 
himself to be something distinct from his ideas 
and impressions; something which continues the 
same identical self, when all his ideas and impres- 
sions are changed. It is impossible to trace the 
origin of this opinion in history : for all languages 
hath it interwoven in their original construction. 
All nations have always believed it. The con- 
stitution of all laws and governments, as well as 
the common transactions of life, suppose it. 

It is no less impossible for any man to recol- 
lect when he himself came by this notion? for, 
as far back as we can remember, we were already 
in possession of it, and as fully persuaded of our 
own existence, and the existence of other things, 
as that one and one make two. It seems therc- 

E 



OQ OF THE HUMAN MIND. [CHAP. 2. 

fore, that this opinion preceded all reasoning, 
and experience, and instruction; and this is the 
more probable, because we could not get it by 
any of these means. It appears then to be an 
undeniable fact, that from thought or sensation, 
all mankind, constantly and invariably, from the 
first dawning of reflection, do infer a power or 
faculty of thinking, and a permanent being or 
mind to which that faculty belongs; and that 
we as invariably ascribe all the various kinds of 
sensation and thought we are conscious of, to 
one individual mind or self. 

But by what rules of logic we make these in- 
ferences, it is impossible to show; nay, it is im- 
possible to show how our sensations and thoughts 
can give us the very notion and conception either 
of a mind or of a faculty. The faculty of smell- 
ing is something very different from the actual 
sensation of smelling; for the faculty may remain 
when we have no sensation. And the mind is no 
less different from the faculty; for it continues 
the same individual being when that faculty is 
lost. Yet this sensation suggests to us both a 
faculty and a mind; and not only suggests the 
notion of them, but creates a belief of their exist- 
ence; although it is impossible to discover, by 
reason, any tie or connection between one and the 
other. 

What shall we say then? Either those infer- 
ences which we draw from our sensations, name- 
ly, the existence of a mind, and of powers or fa- 
culties belonging to it, are prejudices of philoso- 



SECT. 7.] OF SMELLING. & t 

phy or education, mere fictions of the mind, 
which a wise man should throw off as he does 
the belief of fairies; or they are judgments of 
nature, judgments not got by comparing ideas, 
and perceiving agreements and disagreements, 
but immediately inspired by our constitution. 

If this last is the case, as I apprehend it is, 
it will be impossible to shake off those opinions, 
and we must yield to them at last, though we 
struggle hard to get rid of them. And if we 
could by a determined obstinacy, shake off the 
principles of our nature, this is not to act the 
philosopher, but the fool or the madman. It is 
incumbent upon those who think that these are 
not natural principles, to show, in the first place, 
how we can otherwise get the notion of a mind 
and its faculties; and then to show, how we come 
to deceive ourselves into the opinion that sensa- 
tion cannot be without a sentient being. 

It is the received doctrine of philosophers, that 
our notions of relations can only be got by com- 
paring the related ideas; but, in the present 
case, there seems to be an instance to the con- 
trary. It is not by having first the notions of 
mind and sensation, and then comparing them 
together, that we perceive the one to have the 
relation of a subject or substratum, and the other 
that of an act or operation; on the contrary, one 
of the related things, to wit, sensation, suggests 
to us both the correlate and the relation. 

I beg leave to make use of the word suggestion, 
because I know not one more proper to express 
e 2 



6& OF THE HUMAN MIND. [CHAJP. 2* 

a power of the mind, which seems entirely to 
have escaped the notice of philosophers, and to 
which we owe many of our simple notions which 
are neither impressions nor ideas, as well as many 
original principles of belief. I shall endeavour to 
illustrate, by an example, what I understand by 
this word. We all know that a certain kind of 
sound suggests immediately to the mind, a coach 
passing in the street; and not only produces the 
imagination, but the belief, that a coach is pass- 
ing. Yet there is here no comparing of ideas, 
no perception of agreements or disagreements, 
to produce this belief; nor is there the least 
similitude between the sound we hear, and the 
coach we imagine and believe to be passing. 

It is true that this suggestion is not natural and 
original; it is the result of experience and habit. 
But I think it appears, from what hath been said, 
that there are natural suggestions; particularly, 
that sensation suggests the notion of present ex- 
istence, and the belief that what we perceive or 
feel, does now exist; that memory suggests the 
notion of past existence, and the belief that what 
we remember did exist in time past; and that 
our sensations and thoughts do also suggest the 
notion of a mind, and the belief of its existence, 
and of its relation to our thoughts. By a like 
natural principle it is, that a beginning of exist- 
ence, or any change in nature, suggests to us the 
notion of a cause, and compels our belief of its 
existence. And in like manner, as shall be 
shewn when we come to the sense of touch, 



SECT. 8. OF SMELLING. 69 

certain sensations of touch, by the constitution 
of our nature, suggest to us extension, solidity, 
and motion, which are nowise like to sensations, 
although they have been hitherto confounded 
with them. 



SECT. VIII. 



There is a quality or virtue in bodies, which we call 
their smell. How this is connected in the imagi- 
nation with the sensation. 

We have considered smell as signifying a sensa- 
tion, feeling, or impression upon the mind; 
and, in this sense, it can only be in a mind, 
or sentient being: but it is evident, that man- 
kind give the name of smell much more fre- 
quently to something which they conceive to be 
external, and to be a quality of body: they un- 
derstand something by which it does not at all 
infer a mind; and have not the least difficulty in 
conceiving the air perfumed with aromatic odours 
in the desarts of Arabia, or in some uninhabit- 
ed island, where the human foot never trod. 
Every sensible day labourer hath as clear a no- 
tion of this, and as full a conviction of the possi- 
bility of it, as he hath of his own existence; and 
can no more doubt of the one than of the other. 
Suppose that such a man meets with a modern 
philosopher, and wants to be informed, whai 

e.3 






?0 OF THE HUMAN MIND. [CHAP. % 

smell in plants is. The philosopher tells him, 
that there is no smell in plants, nor in any thing, 
but in the mind; that it is impossible there can be 
smell but in a mind; and that all this hath been 
demonstrated by modern philosophy. The plain 
man will, no doubt, be apt to think him merry: 
but if he finds that he is serious, his next con- 
cluson will be, that he is mad; or that philoso- 
phy, like magic, puts men into a new world, and 
gives them different faculties from common men. 
And thus philosophy and common sense are set 
at variance. But who is to blame for it? In my 
opinion the philosopher is to blame. For if he 
means by smell what the rest of mankind most 
commonly mean, he is certainly mad. But if he 
puts a different meaning upon the word, without 
observing it himself, or giving warning to others, 
he abuses language, and disgraces philosophy, 
without doing any service to truth: as if a man 
should exchange the meaning of the words 
daughter and cow, and then endeavour to prove 
to his plain neighbour, that his cow is his daugh- 
ter, and his daughter his cow. 

I believe there is not much more wisdom in 
many of those paradoxes of the ideal philosophy, 
which to plain sensible men appear to be palpable 
absurdities, but with the adepts pass for profound 
discoveries. I resolve, for my own part, always 
to pay a great regard to the dictates of common 
sense, and not to depart from them without ab- 
solute necessity; and therefore I am apt to think, 
that there is really something in the rose or lily, 



SECT. 8.] OF SMELLING. 71 

which is by the vulgar called smell, and which con- 
tinues to exist when it is not smelled : and shall pro- 
ceed to inquire what this is; how w T e come by the 
notion of it; and what relation this quality or vir- 
tue of smell hath to the sensation, which we have 
been obliged to call by the same name, for want 
of another. 

Let us therefore suppose, as before, a person be- 
ginning to exercise the sense of smelling: a little 
experience will discover to him, that the nose is 
the organ of this sense, and that the air, or some- 
thing in the air, is a medium of it. And finding 
by further experience, that when a rose is near, 
he has a certain sensation; when it is removed, 
the sensation is gone; he finds a connection in 
nature betwixt the rose and this sensation. The 
rose is considered as a cause, occasion, or ante- 
cedent, of the sensation; the sensation as an ef- 
fect or consequent of the presence of the rose: 
they are associated in the mind, and constantly 
found conjoined in the imagination. 

But here it deserves our notice, that although 
the sensation may seem more closely related to 
the mind its subject, or to the nose its organ; 
yet neither of these connections operate so power- 
fully upon the imagination, as its connection with 
the rose its concomitant. The reason of this 
seems to be, that its connection with the mind is 
more general, and no way distinguishcth it from 
other smells, or even from tastes, sounds, and 
other kinds of sensation. The relation it hath 
to the organ, is likewise general, and doth no 4 



72 OF THE HUMAN MIND. [CHAP. 2. 

distinguish it from other smells: but the connec- 
tion it hath with the rose is special, and constant; 
by which means they become almost inseparable 
in the imagination, in like manner as thunder and 
lightening, freezing and cold. 



SECT. IX. 



That there is a principlein human nature, Jromwhich 
the notion of this, as 'well as all other natural vir- 
tues or causes, is derived. 

In order to illustrate further how we come to 
conceive a quality or virtue in the rose which we 
call smell, and what this smell is, it is proper to 
observe, that the mind begins very early to thirst 
after principles which may direct it in the exer- 
tion of its powers. The smell of a rose is a cer- 
tain affection or feeling of the mind; and as it is 
not constant, but comes and goes, we want to 
know when and where we may expect it, and are 
uneasy till we find something, which being pre- 
sent, brings this feeling along with it, and being 
removed, removes it. This, when found, we call 
the cause of it; not in a strict and philosophical 
sense: as if the feeling were really effected or 
produced by that cause, but in a popular sense: 
for the mind is satisfied, if there is a constant 
conjunction between them; and such causes are 
in reality nothing else but laws of nature. Hav- 



SECT. 9.] OF SMELLING. JS 

ing found the smell thus constantly conjoined 
with the rose, the mind is at rest, without inquir- 
ing whether this conjunction is owing to a real 
efficiency or not; that being a philosophical in- 
quiry, which does not concern human life. But 
every discovery of such a constant conjunction 
is of real importance in life, and makes a strong 
impression upon the mind. 

So ardently do we desire to find every thing 
that happens within our observation thus con- 
nected with something else, as its cause or occa- 
sion, that we are apt to fancy connections upon 
the slightest grounds: and this weakness is most 
remarkable in the ignorant, who know least of 
the real connections established in nature. A 
man meets with an unlucky accident on a certain 
day of the year; and knowing no other cause of 
his misfortune, he is apt to conceive something 
unlucky in that day of the calendar; and if he 
finds the same connection hold a second time, is 
strongly confirmed in his superstition. I remem- 
ber, many years ago, a white ox was brought in- 
to this country, of so enormous a size, that people 
came many miles to see him. There happened, 
some months after, an uncommon fatality among 
women in child-bearing, Two such uncommon 
events following one another, gave a suspicion of 
their connection, and occasioned a common opi- 
nion among the country people, that the white ox 
was the cause of this fatality. 

However silly and ridiculous this opinion was, 
it sprung from the same root in human nature. 



7^ OF THE HUMAN MIND. [CHAP. %. 

on which all natural philosophy grows; namely, 
an eager desire to find out connections in things, 
and a natural, original, and unaccountable pro- 
pensity to believe, that the connections which we 
have observed in times past, will continue in time 
to come. Omens, portents, good and bad luck, 
palmistry, astrology, all the numerous arts of di* 
vination, and of interpreting dreams, false hypo- 
theses and systems, and true principles in the 
philosophy of nature, are all built upon the same 
foundation in the human constitution; and are 
distinguished only according as we conclude 
rashly from too few instances, or cautiously from 
a sufficient induction. 

As it is experience only that discovers these 
connections between natural causes and their ef- 
fects; without inquiring further, we attribute to 
the cause some vague and indistinct notion of 
power or virtue to produce the effect. And in 
many cases, the purposes of life do not make it 
necessary to. give distinct names to the cause 
and the effect. Whence it happens, that being 
closely connected in the imagination, although 
very unlike to each other, one name serves for 
both; and, in common discourse, is most fre- 
quently applied to that which, of the two, is most 
the object of our attention. This occasions an 
ambiguity in many words, which having the same 
causes in all languages, is common to all, and is 
apt to be overlooked even by philosophers. — 
Some instances will serve both to illustrate and 
confirm wh at we have said. 



SECT. 9.-] OF SMELLING. 7 J 

Magnetism signifies both the tendency of the 
iron towards the magnet, and the power of the 
magnet to produce that tendency: and if it was 
asked, whether it is a quality of the iron or of 
the magnet? one would perhaps be puzzled at 
first; but a little attention would discover, that 
we conceive a power or virtue in the magnet as 
the cause, and a motion in the iron as the effect; 
and although these are things quite unlike, they 
are so united in the imagination, that we srive 
the common name of magnetism to both. The 
same thing may be said of gravitation, which 
sometimes signifies the tendency of bodies to- 
wards the earth, sometimes the attractive power 
of the earth, which we conceive as the cause of 
that tendency. We may observe the same am- 
biguity in some of Sir Isaac Newton's defini- 
tions; and that even in words of his own making. 
In three of his definitions, he explains very dis- 
tinctly what he understands by the absolute quan- 
tity, and what by the accelerative quantity, and 
what by the motive quantity, of a centripetal 
force. In the first of these three definitions, 
centripetal force is put for the cause, which we 
conceive to be some power or virtue in the centre 
or central body : in the two last, the same word 
is put for the effect of this cause, in producing 
velocity, or in producing motion towards that 
centre. 

Heat signifies a sensation, and cold a contrary 
one. But heat likewise signifies a quality or state 
of bodies, which hath no contrary, but different 



76 OF THE HUMAN MIND. [CHAP. %. 

degrees. When a man feels the same water hot 
to one hand, and cold to the other, this gives 
him occasion to distinguish between the feeling, 
and the heat of the body; and although he knows 
that the sensations are contrary, he does not ima- 
gine that the body can have contrary qualities at 
the same time. And when he finds a different 
taste in the same body in sickness and in health, 
he is easily convinced, that the quality in the 
body called taste, is the same as before, although 
the sensations he has from it are perhaps opposite. 
The vulgar are commonly charged by philoso- 
phers, with the absurdity of imagining the smell in 
the rose to be something like to the sensation of 
smelling: but 1 think unjustly, for they neither 
give the same epithets to both, nor do they rea- 
son in the same manner from them. What is 
smell in a rose? It is a quality or virtue of the 
rose, or of something proceeding from it, which 
we perceive by the sense of smelling; and this is 
all we know of the matter. But what is smelling? 
It is an act of the mind, but is never imagined 
to be a quality of the mind. Again, the sensa- 
tion of smelling is conceived to infer necessarily 
a mind or sentient being; but a smell in the rose 
infers no such thing. We say, This body smells 
sweet; that stinks; but we do not say, This mind 
smells sweet, and that stinks. Therefore smell 
in the rose, and the sensation which it causes, 
are not conceived, even by the vulgar, to be 
things of the same kind, although they have the 
same name. 



SECT. 9-3 OF SMELLING. 77 

From what hath been said, we may learn, that 
the smell of a rose signifies two things. First, A 
sensation, which can have no existence but when 
it is perceived, and can only be in a sentient be- 
ing or mind. Secondly, It signifies some power, 
quality, or virtue, in the rose, or in the effluvia 
proceeding from it, which hath a permanent ex- 
istence, independent of the mind, and which by 
the constitution of nature produces the sensation 
in us. By the original constitution of our nature, 
we are both led to believe, that there is a per- 
manent cause of the sensation, and prompted to 
seek after it; and experience determines us to 
place it in the rose. The names of all smells, 
tastes, sounds, as well as heat and cold, have a 
like ambiguity in all languages ; but it deserves 
our attention, that these names are but rarely, in 
common language, used to signify the sensations; 
for the most part, they signify the external qua- 
lities which are indicated by the sensations. The 
cause of which phenomenon I take to be this: 
Our sensations have very different degrees of 
strength. Some of them are so quick and lively 
as to give us a great deal either of pleasure or of 
uneasiness: When this is the case, we are com- 
pelled to attend to the sensation itself, kind to 
make it an object of thought and discourse; we 
give it a name, which signifies nothing but the sen- 
sation; and in this case we readily acknowledge, 
that the thing meant by that name is in the mind 
only, and not in any thing external. Such are 
the various kinds of pain, sickness, and the sen- 



78 OF THE HUMAN MIND. [CHAP. £. 

sations of hunger and other appetites. But where 
the sensation is not so interesting as to require to 
be made an object of thought, our constitution 
leads us to consider it as a sign of something ex- 
ternal, which hath a constant conjunction with 
it; and having found what it indicates, we give 
a name to that: the sensation, having no proper 
name, falls in as accessory to the thing signified 
by it, and it is confounded under the same name. 
So that the name may indeed be applied to the 
sensation, but most properly and commonly is 
applied to the thing indicated by that sensation. 
The sensations of smell, taste, sound and colour, 
are of infinitely more importance as signs or in- 
dications, than they are upon their own account; 
like the words of a language, wherein we do not 
attend to the sound, but to the sense- 



SECT. X. 

Whether in sensation the, mind is active or passive? 

There is one inquiry remains, Whether in smell- 
ing, and in other sensations, the mind is active or 
passive? This possibly may seem to be a question 
about words, or at least of very small impor- 
tance; however, if it lead us to attend more ac- 
curately to the operations of our minds than we 
are accustomed to do, it is upon that very ac- 
count not altogether unprofitable. I think the 



SECT. 10.] OF SMELLING. 79 

opinion of modern philosophers is, that in sensa- 
tion the mind is altogether passive. And this 
undoubtedly is so far true, that we cannot raise 
any sensation in our minds by willing it; and on 
the other hand, it seems hardly possible to avoid 
having the sensation, when the object is present- 
ed. Yet it seems likewise to be true, that in pro- 
portion as the attention is more or less turned to 
a sensation, or diverted from it, that sensation is 
more or less perceived and remembered. Every 
one knows, that very intense pain may be divert- 
ed by a surprise, or by any thing that entirely 
occupies the mind. When we are engaged in 
earnest conversation, the clock may strike by us 
without being heard; at least we remember not 
the next moment that we did hear it. The noise 
and tumult of a great trading city, is not heard 
by them who have lived in it all their days; but it 
stuns those strangers who have lived in the peace- 
ful retirement of the country. Whether therefore 
there can be any sensation where the mind is 
purely passive, 1 will not say; bnt I think we are 
conscious of having given some attention to every 
sensation which we remember, though ever so 
recent. 

No doubt, where the impulse is strong and 
uncommon, it is as difficult to withhold attention, 
as it is to forbear crying out in racking pain, or 
starting in a sudden fright: but how far I 
might be attained by strong resolution and prac- 
tice, is not easy to determine. So that, although 
the Peripatetics had no good reason to sup* 



80 OF THE HUMAN MIND. [CHAP. 2. 

pose an active and a passive intellect, since at- 
tention maybe well enough accounted an act of 
the will; yet I think they come nearer to the 
truth, in holding the mind to be in sensation 
partly passive and partly active, then the mo- 
derns, in affirming it to be purely passive. Sen- 
sation, imagination, memory, and judgment, have 
by the vulgar, in all ages, been considered as 
acts of the mind, The manner in which they 
are expressed, in all languages, shows this. When 
the mind is much employed in them, we say it 
is very active; whereas, if they were impressions 
only, as the ideal philosophy would lead us to 
conceive, we ought in such a case rather to say, 
that the mind is very passive: for I suppose no 
man would attribute great activity to the paper I 
write upon, because it receives variety of cha- 
racters. 

The relation which the sensation of smell bears 
to the memory and imagination of it, and to a 
rnind or subject, is common to all our sensations, 
and indeed to all the operations of the mind: the 
relation it bears to the will, is common to it 
with all the powders of understanding: and the 
relation it bears to that quality or virtue of bodies 
which it indicates, in common to it with the sen- 
sations of taste, hearing, colour, heat, and cold : 
so that what hath been said of this sense, may 
easily be applied to several of our senses, and to 
other operations of the mind; and this, I hope, 
will apologise for our insisting so long upon 
it. 



CHAP. 3.] OF TASTING. 81 

CHAP. III. 



OF TASTING, 



A great part of what hath been said of the 
sense of smelling, is so easily applied to those of 
tasting and hearing, that we shall leave the ap- 
plication entirely to the reader's judgment, and 
save ourselves the trouble of a tedious repetition. 

It is probable that every thing that affects the 
taste, is in some degree soluble in the saliva. It 
is not conceivable how any thing should enter 
readily, and of its own accord, as it were, into 
the pores of the tongue, palate, and fauces, unless 
it had some chemical affinity to that liquor with 
which these pores are always replete. It is there- 
fore an admirable contrivance of nature, that the 
organs of taste should always be moist with a 
liquor which is so universal a menstruum, and 
which deserves to be examined more than it hath 
been hitherto, both in that capacity, and as a me- 
dical unguent. Nature teaches dogs, and other 
animals, to use it in this last way; and its sub- 
serviency both to taste and digestion, shew its 
efficacy in the former. 

It is with manifest design and propriety, that 
the organ of this sense guards the entrance of 
the alimentary canal, as that of smell, the en- 
trance of the canal for respiration. And from 
these organs being placed in such manner, that 

F 



S"2 t)F THE HUMAN MIND. [CHAP. 3. 

every thing that enters into the stomach must un- 
dergo the scrutiny of both senses, it is plain, that 
they were intended by nature to distinguish whole- 
some food from that which is noxious. The 
brutes have no other means of choosing their 
food; nor would mankind, in the savage state. 
And it is very probable, that the smell and taste, 
no way vitiated by luxury or bad habits, would 
rarely, if ever, lead us to a wrong choice of food 
among the productions of nature; although the 
artificial compositions of a refined and luxurious 
cookery, or of chemistry and pharmacy, may of- 
ten impose upon both, and produce things agree- 
able to the taste and smell, which are noxious to 
health. And it is probable, that both smell and 
taste are vitiated, and rendered less fit to peform 
their natural offices, by the unnatural kind of life 
men commonly lead in society. 

These senses are likewise of great use to dis- 
tinguish bodies that cannot be distinguished by 
our other senses, and to discern the changes 
which the same body undergoes, which in many 
cases are sooner perceived by taste and smell than 
by any other means. How many things are there 
in the market, the eating house, and the tavern, 
as well as in the apothecary and chemist's shops, 
which are known to be what they are given out 
to be, and are perceived to be good or bad in 
their kind, only by taste or smell? And how far 
our judgment of things, by means of our senses, 
might be improved by accurate attention to the 
small differences of taste and smell, and other 



CHAP. 3.] OF TASTING. 83 

sensible qualities, is not easy to determine. Sir 
Isaac Newton, by a noble effort of his great 
genius, attempted from the colour of opaque 
bodies, to discover the magnitude of the minute 
pellucid parts, of which they are compounded: 
and who knows what new lights natural philoso- 
phy may yet receive from other secondary quali- 
ties duly examined? 

Some tastes and smell stimulate the nerves, 
and raise the spirits; but such an artificial eleva- 
tion of the spirits is, by the laws of nature, fol- 
lowed by a depression, which can only be reliev- 
ed by time, or by the repeated use of the like 
stimulus. By the use of such things we create 
an appetite for them, which very much resembles 
and hath all the force of a natural one. It is 
in this manner that men acquire an appetite 
for snuff, tobacco, strong liquors, laudanum, and 
the like. 

Nature indeed seems studiously to have set 
bounds to the pleasures and pains we have by 
these two senses, and to have confined them 
within very narrow limits, that we might not 
place any part of our happiness in them; there 
being hardly any smell or taste so disagreable 
that use will not make it tolerable, and at last 
perhaps agreeable; nor any so agreeable as not 
to lose its relish by constant use. Neither is 
there any pleasure or pain of these senses which 
is not introduced, or followed, by some degree 
of its contrary, which nearly balances it. So that 
we .may here apply the beautiful allegory of the 

f2 



84 OF THE HUMAN MIND. CHAP. 3.] 

divine Socrates; That although pleasure and 
pain are contrary in their nature, and their faces 
looked different ways, yet Jupiter hath tied them 
so together, that he that lays hold of the one, 
draws the other along with it. 

As there is a great variety of smells, seeming- 
ly simple and uncompounded, not only altoge- 
ther unlike, but some of them contrary to others; 
and as the same thing may be said of tastes ; it 
would seem that one taste is not less different 
from another than it is from a smell : and there- 
fore it may be a question, how all smells come to be 
considered as one genus, and all tastes as another? 
What is the generical distinction? Is it only that 
the nose is the organ of the one, and the palate 
of the other? or, abstracting from the organ, is 
there not in the sensations themselves something 
common to smells, and something else common 
to tastes, whereby the one is distinguished, from 
the other? It seems most probable that the 
latter is the case; and that under the appearance 
of the greatest simplicity, there is still in these 
sensations something of composition. 

If one considers the matter abstractly, it would 
seem, that a number of sensations, or indeed of 
any other individual things, which are perfectly 
simple and uncompounded, are incapable of 
being reduced into genera and species; because 
individuals which belong to a species, must have 
something peculiar to each, by which they are 
distinguished, and something common to the 
whole species. And the same may be said of 



CHAP. 3-3 GF TASTING. S£ 

species which belongs to one genus. And whether 
this does not imply some kind of composition, 
we shall leave to metaphysicians to determine. 

The sensations both of smell and taste do un- 
doubtedly admit of an immense variety of modi- 
fications, which no language can express. If a 
man was to examine five hundred different wines, 
he would hardly find two of them that had pre- 
cisely the same taste: the same thing holds in 
cheese, and in many other things. Yet of five 
hundred different tastes in cheese or wine, we 
can hardly describe twenty, so as to give a dis- 
tinct notion of them to one who had not tasted 
them. 

Dr. Nehemiah Grew, a most judicious and 
laborious naturalist, in a discourse read before 
the Royal Society, anno 167«5, hath endeavoured 
to show, that there are at least sixteen different 
simple tastes, which he enumerates. How many 
compound ones may be made out of all the vari- 
ous combinations of two, three, four, or more of 
these simple ones, they who are acquainted with 
the theory of combinations will easily perceive. 
All these have various degrees of intenseness and 
weakness. Many of them have other varieties; 
in some the taste is more quickly perceived upon 
the application of the sapid body, in others more 
slowly; in some the sensation is more perma- 
nent, in others more transient; in some it seems 
to undulate, or return after certain intervals, in 
others it is constant: the various parts of the 
organ; as the lips, the tip of the tongue, the root 

f 3 



86 OF THE HUMAN MIND. [CHAP. S. 

of the tongue, the fauces, the uvula, and the 
throat, are some of them chiefly affected by one 
sapid body, and others by another. All these 
and other varieties of tastes, that accurate writer 
illustrates by a number of examples. Nor is it 
to be doubted, but smells, if examined with the 
same accuracy, would appear to have as great 
variety. 



CHAP. 4.] OF HEARING- S? 



CHAP. IV. 



OF HEARING, 



SECT. I. 

Variety of sounds. Their 'place and distance learned 
by custom, without reasoning. 

Sounds have probably no less variety of modifi- 
cations, than either tastes or odours. For, first, 
sounds differ in tone. The ear is capable of per- 
ceiving four or five hundred variations of tone in 
sound, and probably as many different degrees of 
strength; by combining these, we have above 
twenty thousand simple sounds, that differ either 
in tone or strength; supposing every tone to be 
perfect. But it is to be observed, that to make 
a perfect tone, a great many undulations of elas- 
tic air are required, which must all be of equal 
duration and extent, and follow one another with 
perfect regularity; and each undulation must be 
made up of the advance and recoil of innumerable 
particles of elastic air, whose motions are all uni- 
form in direction, force, and time. Hence we 
may easily conceive a prodigious variety in the 
same tone arising from irregularities of it, oc- 
casioned by the constitution, figure, situation, 



38 OF THE HUMAN MIND. [CHAP. 4« 

or manner of striking the sonorous body: from 
the constitution of the elastic medium, or its be- 
ing disturbed by other motions; and from the 
constitution of the ear itself, upon which the 
impression is made. 

A flute, a violin, a hautboy, and a French horn, 
may all sound the same tone, and be easily dis- 
tinguishable. Nay, if twenty human voices sound 
the same note, and with equal strength, there 
will still be some difference. The same voice, 
while it retains its proper distinctions, may yet 
be varied many ways, by sickness or health, 
youth or age, leanness or fatness, good or bad 
humour. The same words spoken by foreigners 
and natives, nay, by persons of different pro- 
vinces of the same nation, may be distinguished. 

Such immense variety of sensations of smell, 
taste and sound, surely was not given us in vain. 
They are signs, by which we know and distin- 
guish things without us; and it was fit that the 
variety of the signs should in some degree cor- 
respond with the variety of things signified by 
them. 

It seems to be by custom, that we learn to 
distinguish both the place of things, and their 
nature, by means of their sound. That such a 
noise is in the street, such another in the room 
above me; that this is a knock at my door, that 
a person walking up stairs, is probably learnt by 
experience. I remember, that once lying a-bed, 
and having been put into a flight, I heard my 
own heart beat; but I took it to be one knock- 



SECT. 1.] OF HEARING. 39 

ing at the door, and arose and opened the door 
oftener than once, before I discovered the sound 
was in my own breast. It is probable, that pre- 
vious to all experience, we should as little know, 
whether a sound came from the right or left, from 
above or below, from a great or a small distance, 
as we should know whether it was the sound of 
a drum or a bell, or a cart. Nature is frugal in 
her operations, and will not be at the expence of 
a particular instinct, to give us that knowledge 
which experience will soon produce, by means of 
a general principle of human nature. 

For a little experience, by the constitution of 
human nature, ties together not only in our ima- 
gination, but in our belief, those things which 
were in their nature unconnected. When I hear 
a certain sound, I conclude immediately without 
reasoning, that a coach passes by. There are no 
premises from which this conclusion is inferred 
by any rules of logic. It is the effect of a prin- 
ciple of our nature, common to us with the 
brutes. 

Although it is by hearing, that we are capable 
of the perception of harmony and melody, and 
of all charms of music; yet it would seem, 
that these require a higher faculty, which we call 
a musical ear. This seems to be in very different 
degrees, in those who have the bare faculty of 
hearing equally perfect; and therefore ought not 
to be classed with the external senses, but in a 
higher order. 



90 <5F THE HUMAN MIND. [CHAP. 4. 

SECT. II. 

Of natural language. 

One of the noblest purposes of sound undoubt- 
edly is language; without which mankind would 
hardly be able to attain any degree of improve- 
ment above the brutes. Language is commonly 
considered as purely an invention of man, who 
by nature are no less mute than the brutes, but 
having a superior degree of invention and reason, 
have been able to contrive artificial signs of their 
thoughts and purposes, and to establish them by 
common consent. But the origin of language 
deserves to be more carefully inquired into, not 
only as this inquiry may be of importance for 
the improvement of language, but as it is related 
to the present subject, and tends to lay open 
some of the first principles of human nature. I 
shall therefore offer some thoughts upon this sub- 
ject. 

By language, I understand all those signs which 
mankind use in order to communicate to others 
their thoughts and intentions, their purposes and 
desires. And such signs may be conceived to be 
of two kinds: First, such as have no meaning, 
but what is affixed to them by compact or agree- 
ment among those who use them; these are arti- 
ficial signs: Secondly, such as, previous to all 
compact or agreement, have a meaning which 



SECT. 2.] OF HEARING. 91 

every man understands by the principles of his 
nature. Language, so far as it consists of arti- 
ficial signs, may be called artificial; so far as it 
consists of natural signs, I call it natural. 

Having premised these definitions, I thiiik it 
is demonstrable, that i^ mankind had not a natu- 
ral language, they could never have invented an 
artificial one by their reason and ingenuity. For 
all artificial language supposes some compact or 
agreement to affix a certain meaning to certain 
signs ; therefore there must be compacts or agree- 
ments before the use of artificial signs; but there 
can be no compact or agreement without signs, 
nor without language ; and therefore there must 
be a natural language before any artificial lan- 
guage can be invented: Which was to be de- 
monstrated. 

Had language in general been a human inven- 
tion, as much as writing or printing, we should 
find whole nations as mute as the brutes. Indeed 
even the brutes have some natural signs by which 
they express their own thoughts, affections, and 
desires; and understand those of others. A 
chick, as soon as hatched, understands the differ- 
ent sounds whereby its dam calls it to food, or 
gives the alarm of danger. A dog or a horse 
understands, by nature, when the human voice 
caresses, and when it threatens him. But brutes, 
as far as we know, have no notion of contracts or 
covenants, or of moral obligation to perform them. 
If nature had given them these notions, she would 
probably have given them natural signs to express 



92 OF THE HUMAN MIND* [CHAP. 4, 

them. And where nature has denied these no- 
tions, it is as impossible to acquire them by art, 
as it is for a blind man to acquire the notion of 
colours. Some brutes are sensible of honour or 
disgrace; they have resentment and gratitude; 
but none of them, as far as we know, can make 
a promise, or plight their faith, having no such 
notions from their constitution. And if mankind 
had not these notions by nature, and natural signs 
to express them by, with all their wit and inge- 
nuity they could never have invented language. 

The elements of this natural language of man- 
kind, or the signs that are naturally expressive of 
our thoughts, may, 1 think, be reduced to these 
three kinds; modulations of the voice, gestures, 
and features. By means of these, two savages, 
who have no common artificial language, can con- 
verse together; can communicate their thoughts 
in some tolerable manner; can ask and refuse, 
affirm and deny, threaten and supplicate; can 
traffic, enter into covenants, and plight their 
faith. This might be confirmed by historical 
facts of undoubted credit, if it were necessary. 

Mankind having thus a common language by 
nature, though a scanty one, adapted only to the 
necessities of nature, there is no great ingenuity 
required in improving it by the addition of arti- 
ficial signs to supply the deficiency of the natural. 
These artificial signs must multiply with the arts 
of life, and the improvements of knowledge. 
The articulations of the voice, seem to be, of all 
signs? the most proper for artificial language ^ 



SECT. 2.] OF SEEING. 93 

and as mankind have universally used them for 
that purpose, we may reasonably judge that nature 
intended them for it. But nature probably does 
not intend that we should lay aside the use of the 
natural signs; it is enough that we supply their 
defects by artificial ones. A man that rides al- 
ways in a chariot, by degrees loses the use of his 
legs; and one who uses artificial signs only, loses 
both the knowledge and use of the natural. 
Dumb people retain much more of the natural 
language than others, because necessity obliges 
them to use it. And for the same reason, sava- 
ges have much more of it then civilized nations. 
It is by natural signs chiefly that we give 4 force 
and energy to language ; and the less language 
has of them, it is the less expressive and persua- 
sive. Thus, writing is less expressive than read- 
ing, and reading less expressive than speaking 
without book: speaking without the proper and 
natural modulations, force, and variations of the 
voice, is a frigid and dead language, compared 
with that which is attended with them ; it is still 
more expressive when we add the language of the 
eyes and features; and is then only in its perfect 
and natural state, and attended with its proper 
energy, when to all these we superadd, the force 
of action. 

Where speech is natural, it will be an exercise 
not of the voice and lungs only, but of all the 
muscles of the body; like that of dumb people 
and savages, whose language, as it has more of 
nature, is more expressive, and is more easily 
learned. 



9£ Or THE HUMAN MIND. [CHAP. 4. 

Is it not pity that the refinements of a civilized 
life, instead of supplying the defects of natural 
language, should root it out, and plant in its 
stead dull and lifeless articulations of unmeaning 
sounds, or the scrawling of insignificant charac- 
ters? The perfection of language is commonly 
thought to be, to express human thoughts and 
sentiments distinctly by these dull signs; but if 
this is the perfection of artificial language, it is 
surely the corruption of the natural. 

Artificial signs signify, but they do not ex- 
press; they speak to the understanding, as alge- 
braical characters may do, but the passions, the 
affections, and the will, hear them not: these 
continue dormant and inactive, till we speak to 
them in the language of nature, to which they 
are all attention and obedience. 

It were easy to show, that the fine arts of the 
musician, the painter, the actor, and the orator, 
so far as they are expressive; although the know- 
ledge of them requires in us a delicate taste, a 
nice judgment, and much study and practice; 
yet they are nothing else but the language of 
nature, which we brought into the world with 
us, but have unlearned by disuse, and so find the 
greatest difficulty in recovering it. 

Abolish the use of articulate sounds and writ- 
ing among mankind for a century, and every man 
would be a painter, an actor, and an orator. We 
mean not to affirm that such an expedient is prac- 
ticable; or, if it were, that the advantage would 
counterbalance the loss; but that, as men are led 



SECT. 2.] OF HEARING. 95 

by nature and necessity to converse together, they 
will use every mean in their power to make them- 
selves understood; and where they cannot do this 
by artificial signs, they will do it, as far as pos- 
sible, by natural ones; and he that understands 
perfectly the use of natural signs, must be the 
best judge in all the expressive art's*. 



9(5 OF THE HUMAN MIND. [CHAP. 5. 



CHAP. V 



OF TOUCH. 



SECT. I. 

Of heat and cold. 

1 he senses which we have hitherto considered, 
are very simple and uniform, each of them exhi- 
biting only one kind of sensation, and thereby 
indicating only one quality of bodies. By the 
ear we perceive sounds, and nothing else; by the 
palate, tastes; and by the nose odours: These 
qualities are all likewise of one order, being all se- 
condary qualities: whereas by touch we perceive 
not one quality only, but many, and those of 
very different kinds. The chief of them are 
heat and cold, hardness and softness, roughness 
and smoothness, figure, salidity, motion, and 
extension. Wc shall consider these in order. 

As to heat and cold, it will easily be allowed 
that they are secondary qualities, of the same or- 
der with smell, taste and sound. And, therefore, 
what hath been already said of smell, is easily 
applicable to them ; that is, that the words heal 
and cold have each of them two significations; 



SECT. 1.] OF TOUCH. 97 

they sometimes signify certain sensations of the 
mind, which can have no existence when they are 
not felt, nor can exist any where but in a mind or 
sentient being; but. more frequently they signify 
a quality in bodies, which by the laws of nature, 
occasions the sensations of heat and cold in us: 
A quality, which, though connected by custom 
so closely with the sensation, that we cannot with- 
out difficulty separate them; yet hath not the 
least resemblance to it, and may continue to exist 
when there is no sensation at all. 

The sensations of heat and cold are perfectly 
known; for they neither are, nor can be, any 
thing else than what we feel them to be; but the 
qualities in bodies which we call heat and cold, 
are unknown. They are only conceived by us, 
as unknown causes or occasions of the sensations 
to which we give the same names. But though 
common sense says nothing of the nature of these 
qualities, it plainly dictates the existence of them ; 
and to deny that there can be heat and cold 
when they are not felt, is an absurdity too gross 
to merit confutation. For what could be more 
absurd, than to say, that the thermometer cannot 
rise or fall, unless some person be present, or 
that the coast of Guinea would be as cold as 
Nova Zembla, if it had no inhabitants? 

It is the business of philosophers to investigate, 
by proper experiments and induction, what heat 
and cold are in bodies. And whether they make 
heat a particular element diffused through na- 
ture, and accumulated in the heated bodv, or 



9$ OF THE HUMAN MIND. [CHAP. 5. 

whether they make it a certain vibration of the 
parts of the heated body; whether they deter- 
mine that heat and cold are contrary qualities, 
as the sensations undoubtedly are contrary, or 
that heat only is a quality, and cold is privation; 
these questions are within the province of philo- 
sophy: for common sense says nothing on the one 
side or the other. 

But whatever be the nature of that quality in 
bodies which we call heat, we certainly know this, 
that it cannot in the least resemble the sensation 
of heat. It is no less absurd to suppose a like- 
ness between the sensation and the quality, than 
it would be to suppose, that the pain of the gout 
resembles a square or a triangle. The simplest 
man that hath common sense, does not imagine 
the sensation of heat, or any thing that resembles 
that sensation, to be in the fire. He only ima- 
gines, that there is something in the fire, which 
makes him and other sentient beings feel heat. 
Yet as the name of heat, in common language, 
more frequently and more properly signifies this 
unknown something in the fire, than the sensa- 
tion occasioned by it, he justly laughs at the 
philosopher, who denies that there is any heat in 
the fire, and thinks that he speaks contrary to 
common sense. 



SECT. 2.] OF TOUCH. 99 

SECT. II. 

Of hardness and softness. 

Let us next consider hardness and softness; by 
which words we always understand real proper- 
ties or qualities of bodies of which we have a dis- 
tinct conception. 

When the parts of a body adhere so firmly that 
it cannot easily be made to change its figure, we 
call it hard; when its parts are easily displaced, 
we call it soft This is the notion which all man- 
kind have of hardness and softness: they are 
neither sensations, nor like any sensation; they 
were real qualities before they were perceived by 
touch, and continue to be so when they are not 
perceived: for if any man will affirm, that dia- 
monds were not hard till they were handled, who 
would reason with him? 

There is, no doubt, a sensation by which we 
perceive a body to be hard or soft. This sensa- 
tion of hardness may easily be had, by pressing 
one's hand against the table, and attending to the 
feeling that ensues, setting aside, as much as 
possible, all thought of the table and its qualities, 
or of any external thing. But it is one thing to 
have the sensation, and another to attend to it y 
and make it a distinct object of reflection. The 
first is very easy; the last, in most cases, ex- 
tremely difficult. 

g 2 



100 OF THE HUMAN MIND. [CHAP. 5. 

We are so accustomed to use the sensation as 
a sign, and to pass immediately to the hardness 
signified, that, as far as appears, it was never 
made an object of thought, either by the vulgar 
or by philosophers; nor has it a name in any 
language. There is no sensation more distinct, 
or more frequent; yet it is never attended to, but 
passes through the mind instantaneously, and 
serves only to introduce that quality in bodies, 
which, by a law of our constitution, it sug- 
gests. 

There are, indeed, some cases, wherein it is no 
difficult matter to attend to the sensation occa- 
sioned by the hardness of a body; for instance, 
when it is so violent as to occasion considerable 
pain: then nature calls upon us to attend to it, 
and then we acknowledge, that it is a mere sens- 
ation, and can only be in a sentient being. If a 
man run his head with violence against a pillar, 
I appeal to him, whether the pain he feels re- 
sembles the hardness of the stone; or if he can 
conceive any thing like what he feels, to be an 
inanimate piece of matter. 

The attention of the mind is here entirely 
turned towards the painful feeling; and, to speak 
in the common language of mankind, he feels 
nothing in the stone, but feels a violent pain in 
his head. It is quite otherwise when he leans his 
head gently against the pillar; for then he will 
tell you that he feels nothing in his head, but 
feels hardness in the stone. Hath he not a sensa- 
tion in this case as well as in the other? Un- 



SECT. 2.] OF TOUCH. 101 

doubtedly he hath: but it is a sensation which 
nature intended only as a sign of something in the 
stone; and, accordingly, he instantly fixes his at- 
tention upon the thing signified; and cannot, 
without great difficulty, attend so much to the 
sensation, as to be persuaded that there is any 
such thing distinct from the hardness it signifies. 

But however difficult it may be to attend to 
this fugitive sensation, to stop its rapid progress, 
and to disjoin it from the external quality of 
hardness, in whose shadow it is apt immediately 
to hide itself: this is what a philosopher by pains 
and practice must attain, otherwise it will be im- 
possible for him to reason justly upon this sub- 
ject, or even to understand what is here advan- 
ced. For the last appeal, in subjects of this na- 
ture, must be to what a man feels and perceives 
in his own mind. 

It is indeed strange that a sensation which we 
have every time w r e feel a body hard, and which, 
consequently, we can command as often', and 
continue as long as we please, a sensation as dis- 
tinct and determinate as any other, should yet be 
so much unknown, as never to have been made 
an object of thought and reflection, nor to have 
been honoured with a name in any language; 
that philosophers, as well as the vulgar, should 
have entirely overlooked it, or confounded it with 
that quality of bodies which we call hardness, to 
which it hath not the least similitude. May we 
not hence conclude, that the knowledge of the 
human faculties is but in its infancy? That we 

g 3 



102 OF THE HUMAN MIND. [CHAP. 5. 

have not yet learned to attend to those operations 
of the mind, of which we are conscious every hour 
of our lives? That these are habits of inattention 
acquired very early, which are as hard to be over- 
come as other habits? For I think it is probable, 
that the novelty of this sensation will procure 
some attention to it in children at first; but be- 
ing in nowise interesting in itself, as soon as it 
becomes familiar, it is overlooked, and the atten- 
tion turned solely to that which it signifies. — 
Thus, when one is learning a language, he at- 
tends to the sounds; but when he is master of it, 
he attends only to the sense of what he would 
express. If this is the case, we must become as 
little children again, if we will be philosophers: 
we must overcome this habit of inattention which 
has been gathering strength ever since we began 
to think; a habit, the usefulness of which, in 
common life, atones for the difficulty it creates 
to the philosopher, in discovering the first prin- 
ciples of the human mind. 

The firm cohesion of the parts of a body, is no 
more like that sensation by which 1 perceive it 
to be hard, than the vibration of a sonorous body 
is like the sound I hear: nor can I possibly per- 
ceive, by my reason, any connection between the 
one and the other. No man can give a reason, 
why the vibration of a body might not have given 
the sensation of smelling, and the effluvia of 
bodies affected our liearing, if it had so pleased 
our Maker. In like manner, no man can give a 
reason, why tire sensation of smell, or taste, or 



SECT. 2.] OV TOUCH. 103 

sound, might not have indicated hardness, as well 
as that sensation, which, by our constitution, 
does indicate it. Indeed, no man can conceive 
any sensation to resemble any known quality of 
bodies. Nor can any man shew, by any good 
argument, that all our sensations might not have 
been as they are, though no body, nor quality of 
body, had ever existed. 

Here, then, is a phenomenon of human nature, 
which comes to be resolved. Hardness of bodies 
is a thing that we conceive as distinctly, and be- 
lieve as firmly, as any thing in nature. We have 
no way of coming at this conception and belief, 
but by means of a certain sensation of touch, to 
which hardness hath not the least similitude; 
nor can we, by any rules of reasoning, infer the 
one from the other. The question is, How we 
come by this conception and belief? 

First, as to the conception : shall we call it an 
idea of sensation or of reflection? The last will 
not be affirmed; and as little can the first, unless 
we call that an idea of sensation, which hath no 
resemblance to any sensation. So that the origin 
of this idea of hardness, one of the most common 
and most distinct we have, is not to be found in 
all our systems of the mind: not even in those 
which have so copiously endeavoured to deduce 
all our notions from sensations and reflection. 

But, secondly, supposing we have got the con- 
ception of hardness, how come we by the belief 
of it? It is self-evident, from comparing the 
ideas, that such a sensation could not be felt, 



104 OF THE HUMAN MIND. [CHAP. 5. 

unless such a quality of bodies existed? No. 
Can it be proved by probable or certain argu- 
ments? No, it cannot. Have we got this belief, 
then, by tradition, by education, or by experience? 
No, it is not got in any of these ways. Shall we 
then throw off this belief, as having no founda- 
tion in reason? Alas! it is not in our power; 
it triumphs over reason, and laughs at all the ar^ 
guments of a philosopher. Even the author of 
the Treatise of Human Nature, though he saw no 
reason for this belief, but many against it, could 
hardly conquer it in his speculative and solitary 
moments; at other times he fairly yielded to it, 
and confesses that he found himself under a ne- 
cessity to do so. 

What shall we say then of this conception, and 
this belief, which are so unaccountable and un- 
tractable? I see nothing left, but to conclude, 
that by an original principle of our constitution, 
a certain sensation of touch both suggests to the 
mind the conception of hardness, and creates the 
belief of it: or, in other words, that this sensa- 
tion is a natural sign of hardness. And this I 
shall endeavour more fully to explain. 



SECT. 3.] OF TOUCH. 105 

SECT. III. 

Of natural signs. 

As in artificial signs there is often neither simi- 
litude between the sign and thing signified, nor 
any connection that arises necessarily from the 
nature of the things; so it is also in natural signs. 
The word gold has no similitude to the substance 
signified by it ; nor is it in its own nature more 
fit to signify this than any other substance: yet, 
by habit and custom, it suggests this and no 
other. In like manner, a sensation of touch sug- 
gests hardness, although it hath neither simili- 
tude to hardness, nor, as far as we can perceive, 
any necessary connection with it. The differ- 
ence betwixt these two signs lies only in this, 
that, in the first, the suggestion is the effect of 
habit and custom; in the second, it is not the ef- 
fect of habit, but of the original constitution of 
our minds. 

It appears evident from what hath been said 
on the subject of language, that there are natu- 
ral signs, as well as artificial; and particularly. 
That the thoughts, purposes and dispositions of 
the mind, have their natural signs in the features 
of the face, the modulation of the voice, and the 
motion and attitude of the body: That without 
a natural knowledge of the connection between 
these signs and the thing signified by them, 



106 OF THE HUMAN MIND. [CHAP. 5. 

language could never have been invented and 
established among men: and, That the fine arts 
are all founded upon this connection, which we 
may call the natural language of mankind. It is 
now proper to observe, that there are different 
orders of natural signs, and to point out the dif- 
ferent classes into which they may be distinguish- 
ed, that we may more distinctly conceive the re- 
lation between our sensations and the things they 
suggest, and what we mean by calling sensations 
signs of external things. 

The first class of natural signs comprehends 
those whose connection with the thing signified 
is established by nature, but discovered only by 
experience. The whole of genuine philosophy 
consists in discovering such connections, and re- 
ducing them to general rules, The great Lord 
Verulam had a perfect comprehension of this, 
when he called it an interpretation of nature. No 
man'ever more distinctly understood, or happily 
expressed, the nature and foundation of the 
philosophic art. What is all we know of me- 
chanics, astronomy, and optics, but connections 
established by nature, and discovered by expe- 
rience or observation, and consequences deduced 
from them? All the knowledge we have in agri- 
culture 3 gardening, chemistry, and medicine, is 
built upon the same foundation. And if ever 
our philosophy concerning the human mind is 
carried so far as to deserve the name of science, 
which ought never to be despaired of, it must be 
hy observing facts, reducing them to general 



SECT. 3.] OF TOUCft. 107 

rules, and drawing just conclusions from them- 
What we comm,only call natural causes, might, 
with more propriety, be called natural signs, and 
what we call effects, the things signified. The 
causes have no proper efficiency or casualty, as 
far as we know; and all we can certainly affirm is, 
that nature hath established a constant conjunc- 
tion between them and the things called their ef- 
fects; and hath given to mankind a disposition to 
observe those connections, to confide in their 
continuance, and to make use of them for the 
improvement of our knowledge, and increase of 
our power. 

A second class is that wherein the connection 
between the sign and thing signified, is not onlv 
established by nature, but discovered to us by a 
natural principle, without reasoning or experi- 
ence. Of this kind are the natural signs of hu- 
man thoughts, purposes, and desires, which have 
been already mentioned as the natural language 
of mankind. An infant may be put into a fright 
by an angry countenance, and soothed again by 
smiles and blandishments. A child that has a 
good musical ear, may be put to sleep or to dance, 
may be made merry or sorrowful, by the modu- 
lations of musical sounds. The principles of all 
the fine arts, and of what we call a jine taste, 
may be resolved into connections of this kind. 
A fine taste may be improved by reasoning and 
experience; but if the first principles of it were 
not planted in our minds by nature, it couid never 
be acquired. Nay, we have already made it ap- 



108 OF THE HUMAN MIND. [CHAP. 5. 

pear, that a great part of this knowledge, which 
we have by nature, is lost by the disuse of natural 
signs, and the substitution of artificial in their 
place. 

A third class of natural signs comprehends 
those which, though we never before had any 
notion or conception of the things signified, do 
suggest it, or conjure it up, as it were, by a na- 
tural kind of magic, and at once give us a con- 
ception, and create a belief of it. I shewed for- 
merly, that our sensations suggest to us a sentient 
being or mind to which they belong: a being 
which hath a permanent existence, although the 
sensations are transient and of short duration : a 
being which is still the same, while its sensations 
and other operations are varied ten thousand 
ways: a being which hath the same relation to 
all that infinite variety of thoughts, purposes, ac- 
tions, affections, enjoyments, and sufferings, 
which we are conscious of, or can remember. 
The conception of a mind is neither an idea of 
sensation nor of reflection; for it is neither like 
any of our sensations, nor like any thing we are 
conscious of. The first conception of it, as well 
as the belief of it, and of the common relation it 
bears to all that we are conscious of, or remem- 
ber, is suggested to every thinking being, we do 
not know how. 

The notion of hardness in bodies, as well as 
the belief of it, are got in a similar manner; be- 
ing, by an original principle of our nature, an- 
nexed to that sensation which we have when we 



SECT. 3.] OF TOUCH. 109 

feel a hard body. And so naturally and neces- 
sarly does the sensation convey the notion and 
belief of hardness, that hitherto they have been 
confounded by the most acute inquirers into the 
principles of human nature, although ihey appear 
upon accurate reflection, not only to be different 
things, but as unlike as pain is to the point of a 
sword. 

It may be observed, that as the first class of 
natural signs I have mentioned, is the foundation 
of true philosophy, and the second, the founda- 
tion of the fine arts, or of taste; so the last is the 
foundation of common sense ; a part of human 
nature which hath never been explained. 

I take it for granted, that the notion of hard- 
ness and the belief of it, is first got by means of 
that particular sensation, which, as far back as 
we can remember, does invariably suggest it; 
and that if we had never had such a feeling we 
should never have had any notion of hardness. 
I think it is evident, that we cannot by reason- 
ing from our sensations, collect the existence of 
bodies at all, far less any of their qualities. This 
Lath been proved by unanswerable arguments by 
the Bishop of Cloyne, and by the author of the 
Treatise of Human Nature. It appears as evi- 
dent, that this connection between bur sensations 
and the conception and belief of external exis- 
tences, cannot be produced by habit, experience, 
education, or any principle of human nature that 
hath been admitted by philosophers. At the' 
same time it is a fact, that such sensations are 



110 OF THE HUMAN MIND. [CHAP. 5* 

invariably connected with the conception and 
belief of external existences. Hence, by all rules 
of just reasoning, we must conclude, that this 
connection is the effect of our constitution, and 
ought to be considered as an original principle of 
human nature, till we find some more general 
principle into which it may be resolved. 



SECT. IV. 

Of hardness, and other primary qualities. 

Further I observe, that hardness is a quality, 
of which we have as clear and distinct a concep- 
tion as of any thing whatsoever. The cohesion 
of the parts of a body with more or less force, is 
perfectly understood, though its cause is not: we 
know what it is, as well as how it effects the 
touch. It is therefore a quality of a quite differ- 
ent order from those secondary qualities we have 
already taken notice of, whereof we know no 
more naturally, than that they are adapted to raise 
certain sensations in us. If hardness were a qua- 
lity of the same kind, it would be a proper in- 
quiry for philosophers, What hardness in bodies 
is? and we should have had various hypothesis 
about it, as well as about colour and heat. But 
it is evident that any such hypothesis would be 
ridiculous. If any man should say, that hardness 
in bodies is a certain vibration of their parts, or 



SECT. 4.] OF TOt'CH. Ill 

that it is certain effluvia emitted by them which 
effect our touch in the manner we feel; such hy- 
pothesis would shock common sense? because 
we all know, that if the parts of a body adhere 
strongly, it is hard, although it should neither 
emit effluvia, nor vibrate. Yet at the same time, 
no man can say, but that effluvia, or the vibra- 
tion of the parts of a body, might have affected 
our touch, in the same manner that hardness 
now does, if it had so pleased the Author of our 
nature: and if either of these hypothesis is ap- 
plied to explain a secondary quality, such as smell, 
or taste, or sound, or colour, or heat, there ap- 
pears no manifest absurdity in the supposition. 

The distinction betwixt primary and secondary 
qualities hath had several revolutions. Demo- 
critus and Epicurus, and their followers,- main- 
tained it. Aristotle and the Peripatetics abo- 
lished it. Des Cartes, Malebranche, and 
Locke, revived it, and were thought to have put 
it in a very clear light. But Bishop Berkeley 
again discarded this distinction, by such proofs 
as must be convincing to those that hold the re- 
ceived doctrine of ideas. Yet, after all, there 
appears to be a real foundation for it in the prin- 
ciples of our nature. 

What hath been said of hardness, is so easily 
applicable, not only to its opposite, softness, but 
likewise to roughness and smoothness, to figure 
and motion, that we may be excused from mak- 
ing the application, which would only be a repe- 
itioji of what hath been Sy^id. All these, by 



112 



OF THE HUMAN MIND. 



CHAP. 5. 



means of certain corresponding sensations of 
touch, are presented to the mind as real external 
qualities; the conception and the belief of them 
are invariably connected with the corresponding 
sensations, by an original principle of human na- 
ture. Their sensations have no name in any lan- 
guage; they have not only been overlooked by 
the vulgar, but by philosophers ; or if they have 
been at all taken notice of, they have been con- 
founded with the external qualities which they 



suggest. 



SECT. V. 



Of extension. 



It is further to be observed, that hardness and 
softness, roughness and smoothness, figure and 
motion, do all suppose extension, and cannot be 
conceived without it; yet I think it must, on the 
other hand, be allowed, that if we had never felt 
any thing hard or soft, rough or smooth, figured 
or moved, we should never have had a concep- 
tion of extension : so that as there is good ground 
to believe, that the notion of extension could not 
be prior to that of other primary qualities: so it 
is certain that it could not be posterior to the 
notion of any of them being necessarily implied 
in them all. 



SECT. 5.] OF TOUCH. 113 

Extension, therefore, seems to be a quality 
suggested to us, by the very same sensations 
which suggest the other qualities above mention- 
ed. When I grasp a ball in my hand, I perceive 
it at once hard, figured and extended. The feel- 
ing is very simple, and hath not the least resem- 
blance to any quality of body. Yet it suggests 
to us three primary qualities perfectly distinct 
from one another, as well as from the sensation 
which indicates them. When I move my hand 
along the table, the feeling is so simple, that I 
find it difficult to distinguish it into things of dif- 
ferent natures ; yet it immediately suggests hard- 
ness, smoothness, extension, and motion, things 
of very different natures, and all of them as dis- 
tinctly understood as the feeling which suggests 
them. 

We are commonly told by philosophers, that we 
get the idea of extension by feeling along the ex- 
tremities of a body, as if there was no manner of 
difficulty in the matter. I have sought, with 
great pains, I confess, to find out how this idea 
can be got by feeling, but I have sought in vain. 
Yet it is one of the clearest and most distinct 
notions we have; nor is there any thing whatso- 
ever, about which the human understanding can 
carry on so many long and demonstrated trains of 
reasoning. 

The notion of extension is so familiar to us 
from infancy, and constantly obtruded by every 
thing we see and feel, that we are apt to think it 
obvious how it comes into the mind; but upon a 

H 



114 OF THE HUMAN MIND. [CHAP. 5. 

narrower examination we shall find it utterly in- 
explicable. It is true we have feelings of touch, 
which every moment present extension to the 
mind; but how they come to do so, is the ques- 
tion ; for those feelings do no more resemble ex- 
tension, than they resemble justice or courage: 
nor can the existence of extended things be in- 
ferred from those feelings by any rules of reason- 
ing: so that the feelings we have by touch, can 
neither explain how we get the notion, nor how 
we come by the belief of extended things. 

What hath imposed upon philosophers in this 
matter, is, that the feelings of touch, which sug- 
gest primary qualities, have no names, nor are 
they ever reflected upon. They pass through the 
mind instantaneously, and serve only to introduce 
the notion and belief of external things, which by 
our constitution are connected with them. They 
are natural signs, and the mind immediately passes 
to the thing signified, without making the least 
.reflection upon the sign, or observing that there 
was any such thing. Hence it hath always been 
taken for granted, that the ideas of extension, 
figure and motion, are ideas of sensation, which 
enter into the mind, by the sense of touch, in the 
same manner as the sensations of sound and smell 
do by the ear and nose. The sensations of touch 
are so connected, by our constitution, with the 
notions of extension, figure, and motion, that 
philosophers have mistaken the one for the other, 
and never have been able to discern that they 
^vere not only distinct things, but altogether un- 



SECT. 5. OF TOUCH. 115 

like. However, if we will reason distinctly upon 
this subject, we ought to give names to those 
feelings of touch; we must accustom ourselves to 
attend to them, and to reflect upon them, that 
we may be able to disjoin them from, and to 
compare them with, the qualities signified or sug- 
gested by them. 

The habit of doing this is not to be attained 
without pains and practice; and till a man hath 
acquired this habit, it will be impossible for him 
to think distinctly, or to judge right, upon this 
subject. 

Let a man press his hand against the table : 
he feels it hard. But what is the meaning of this? 
the meaning undoubtedly is, that he hath a cer- 
tain feeling of touch, from which he concludes 
without any reasoning, or comparing ideas, that 
there is something external really existing, whose 
parts stick so firmly together, that they cannot 
be displaced without considerable force. 

There is here a feeling and a conclusion drawn 
from it, or some way suggested by it. In order 
to compare these, we must view them separately, 
and then consider by what tie they are connected, 
and wherein they resemble one another. The 
hardness of the table is the conclusion, the feel- 
ing is the medium by which we are led to that 
conclusion. Let a man attend distinctly to this 
medium, and to the conclusion, and he will per- 
ceive them to be as unlike as any two things in 
nature. The one is a sensation of the mind, 
which can have no existence but in a sentient 

h 2 



110 OF THE HUMAN MIND. [CHAP. 5. 

being; nor can it exist one moment longer than 
it is felt; the other is in the table, and we con- 
clude, without any difficulty, that it was in the 
table before it was felt, and continues after the 
feeling was over. The one implies no kind of ex- 
tension, nor parts, nor cohesion; the other im- 
plies all these. Both indeed admit of degrees; 
and the feeling, beyond a certain degree, is a 
species of pain; but adamantine hardness does 
not imply the least pain. 

And as the feeling hath no similitude to hard- 
ness, so neither can our reason perceive the least 
tie or connection between them; nor will the lo- 
gician ever be able to shew a reason why we 
should conclude hardness from this feeling rather 
than softness, or any other quality whatsoever. 
But in reality all mankind are led by their con- 
stitution to conclude hardness from this feeling. 

The sensation of heat, and the sensation we 
have by pressing a hard body, are equally feel- 
ings; nor can we by reason draw any conclusion 
from the one, but what may be drawn from the 
other: but, by our constitution, we conclude 
from the first an obscure or occult quality, of 
which we have only this relative conception, that 
it is something adapted to raise in us the sensa- 
tion of heat; from the second, we conclude a 
quality of which we have a clear and distinct 
conception, to wit, the hardness of the body. 



SECT. 6»] OF TOUCH. 117 

SECT. VI. 

Of extension. 

To put this matter in another light, it may be 
proper to try, whether from sensation alone we 
can collect any notion of extension, figure, mo- 
tion, and space. I take it for granted, that a 
blind man hath the same notions of extension, 
figure, and motion, as a man that sees; that Dr. 
Saunderson had the same notion of a cone, a 
cylinder, and a sphere, and of the motions and 
distances of the heavenly bodies, as Sir Isaac 
Newton. 

As sight, therefore, is not necessary for our 
acquiring those notions, we shall leave it out al- 
together in our inquiry into the first origin of 
them; and shall suppose a blind man, by some 
strange distemper, to have lost all the experience 
and habits and notions he had got by touch; nor 
to have the least conception of the existence, fi- 
gure, dimensions, or extension, either of his own 
body, or of any other; but to have all his know- 
ledge of external things to acquire anew, by 
means of sensation, and the power of reason, 
which we suppose to remain entire. 

We shall, first, suppose his body fixed immove- 
able in one place, and that he can only have the 
feelings of touch, by the application of other bo- 
dies to it. Suppose him first to be pricked with 

h3 



118 OF THE HUMAN MIND. [CHAP. 5. 

a pin; this will, no doubt, give a smart sensation: 
he feels pain; but what can he infer from it? 
Nothing surely with regard to the existence or 
figure of a pin. He can infer nothing from this 
species of pain, which he may not as well infer 
from the gout or sciatica. Common sense may 
lead him to think that this pain has a cause: but 
whether this cause is body or spirit, extended or 
unextended, figured or not figured, he cannot 
possibly, from any principles he is supposed to 
have, from the least conjecture. Having had 
formerly no notion of body or of extension, the 
prick of a pin can give him none. 

Suppose, next, a body not pointed, but blunt, 
is applied to his body with a force gradually in- 
creased until it bruises him. What has he got 
by this, but another sensation, or train of sensa- 
tions, from which he is able to conclude as little 
as from the former? A scirrhous tumour in any 
inward part of the body, by pressing upon the 
adjacent parts, may give the same kind of sensa- 
tion as the pressure of an external body, without 
conveying any notion but that of pain, which 
surely hath no resemblance to extension. 

Suppose, thirdly, that the body applied to him 
touches a larger or a lesser part of his body. 
Can this give him any notion of its extension or 
dimensions? To me it seems impossible that it 
should, unless he had some previous notion of 
the dimensions and figure of his own body, to 
serve him as a measure. When my two hands 
touch the extremities of a body; if I know them 



6ECT. 6.] OP TOUCH. 119 

to be a foot asunder, I easily collect that the body 
is a foot long; and if I know them to be five feet 
asunder, that it is five feet long; but if I know 
not what the distance of my hand is, I cannot 
know the length of the object they grasp; and if 
I have no previous notion of hands at all, or of 
distance between them, I can never get that no- 
tion by their being touched. 

Suppose, again, that a body is drawn along his 
hands or face, while they are at rest: Can this 
give him any notion of space or motion? It no 
doubt gives a new feeling; but how it should 
convey a notion of space or motion, to one who 
had none before, I cannot conceive. The blood 
moves along the arteries and veins, and this mo- 
tion, when violent, is felt: but I imagine no mail', 
by this feeling, could get the conception of space 
or motion, if he had it not before. Such a motion 
may give a certain succession of feelings, as the 
cholic may do; but no feelings, nor any combin- 
ation of feelings, can ever resemble space or 
motion. 

Let us next suppose, that he makes some in*. 
stinctive effort to move his head or his hand; 
but that no motion follows, either on account of 
external resistance, or of palsy. Can this effort 
convey the notion of space and motion to one 
who never had it before? Surely it cannot. 

Last of all let us suppose, that he moves a limb 
by instinct, without having had any previous no- 
tion of space or motion. He has here a new 
sensation, which accompanies the flexure of 



120 OF THE HUMAN MIND. CHAP. 5. J 

joints, and the swelling of muscles. But how this 
sensation can convey into his mind the idea of 
space and motion, is still altogether mysterious 
and unintelligible. The motions of the heart and 
lungs are all performed by the contraction of 
muscles, yet give no conception of space or mo- 
tion. An embryo in the womb has many such 
motions, and probably the feelings that accom- 
pany them, without any idea of space or mo- 
tion. 

Upon the whole, it appears, that our philoso- 
phers have imposed upon themselves, and upon 
us, in pretending to deduce from sensation the 
first origin of our notions of external existences, 
of space, motion, and extension, and all the pri- 
mary qualities of body, that is, the qualities where- 
of we have the most clear and distinct conception. 
These qualities do not at all tally with any sys. 
tern of the human faculties that hath been ad- 
vanced. They have no resemblance to any sensa- 
tion, or to any operation of our minds; and there- 
fore they cannot be ideas either of sensation, or 
of reflection. The very conception of them is ir- 
reconcilable to the principles of all our philoso- 
phic systems of the understanding. The belief 
of them is no less so. 



SECT, 7.] OF TOUCH, KM 

SECT. VII. 

Of the existence of a material world. 

It is beyond our power to say, when or in what 
order we came by our notions of these qualities. 
When w r e trace the operations of our minds as 
far back as memory and reflection can carry us, 
we find them already in possession of our imagi- 
nation and belief, and quite familiar to the mind; 
but how they came first into its acquaintance, 
or what has given them so strong a hold of our 
belief, and what regard they deserve, are no doubt 
very important questions in the philosophy of 
human nature. 

Shall w T e, with the Bishop of Cloyne, serve them 
with a Quo xvarranto, and have them tried at the 
bar of philosophy, upon the statute of the ideal 
system? Indeed, in this trial they seem to have 
come off very pitifully. For although they had 
very able counsel, learned in the law, viz. Des 
Cartes, Malebranciie, and Locke, who said 
every thing they could for their clients; the 
Bishop of Cloyne, believing them to be aiders 
and abetters of heresy and schism, prosecuted 
them witli great vigour, fully answered all that 
had been pleaded in their defence, and silenced 
their ablest advocates, who seem for half a cen- 
tury past to decline the argument, and to trust to 



122 OF THE HUMAN MIND. [CHAP. 5. 

the favour of the jury rather than to the strength 
of their pleadings. 

Thus, the wisdom of philosophy is set in oppo- 
sition to the common sense of mankind. The first 
pretends to demonstrate a priori, that there can 
be no such thing as a material world; that sun, 
moon, stars, and earth, vegetable and animal 
bodies, are, and can be nothing else, but sensa- 
tions in the mind, or images of those sensations 
in the memory and imagination; that, like pain 
and joy, they can have no existence when they 
are not thought of. The last can conceive no 
otherwise of this opinion, than as a kind of meta- 
physical lunacy; and concludes, that too much 
learning is apt to make men mad; and that the 
man who seriously entertains this belief, though 
in other respects he may be a very good man, as a 
man may be who believes that he is made of glass; 
yet surely he hath a soft place in his understand- 
ing, and hath been hurt by much thinking. 

This opposition betwixt philosophy and com- 
mon sense, is apt to have a very unhappy influ- 
ence upon the philosopher himself. He sees 
human nature in an odd, unamiable, and morti- 
fying light. He considers himself, and the rest 
of his species, as born under a necessity of believ- 
ing ten thousand absurdities and contradictions, 
and endowed with such a pittance of reason, as 
is just sufficient to make this unhappy discovery: 
and this is all the fruit of his profound specula- 
tions. Such notions of human nature tend to 
slacken every nerve of the soul, to put every 



SECT. 7.] OP TOUCH. 123 

noble purpose and sentiment out of countenance, 
and spread a melancholy gloom over the whole 
face of things. 

If this is wisdom, let me be deluded with the 
vulgar. I find something within me that recoils 
against it, and inspires more reverent sentiments 
of the human kind, and of the universal adminis- 
tration. Common sense and reason have both 
one author; that almighty Author, in all whose 
other works we observe a consistency, uniformity, 
and beauty, which charm and delight the under- 
standing: there must therefore be some order 
and consistency in the human faculties, as well 
as in other parts of his workmanship. A man 
that thinks reverently of his own kind, and es- 
teems true wisdom and philosophy, will not be 
found, nay, will be very suspicious, of such strange 
and paradoxical opinions. If they are false, .they 
disgrace philosophy; and if they are true, they 
degrade the human species, and make us justly 
ashamed of our frame. 

To what purpose is it for philosophy to decide 
against common sense in this or any other mat- 
ter? The belief of a material world is older, and 
of more authority, than any principles of philoso- 
phy. It declines the tribunal of reason, and 
laughs at all the artillery of the logician. It re- 
tains its sovereign authority in spite of all the 
edicts of philosophy, and reason itself must stoop 
to its orders. Even those philosophers who have 
disowned the authority of our notions of an ex- 
ternal material world, confess, that they find 



124 OF THE HUMAN MIND. [CHAP. 5. 

themselves under a necessity of submitting to 
their power. 

Methinks, therefore, it were better to make a 
virtue of necessity; and, since we cannot get rid 
of the vulgar notion and belief of an external 
world, to reconcile our reason to it as well as we 
can: for if Reason should stomach and fret ever 
so much at this yoke, she cannot throw it off; if 
she will not be the servant of Common Sense, 
she must be her slave. 

In order, therefore, to reconcile reason to com- 
mon sense in this matter, I beg leave to offer to 
the consideration of philosophers these two ob- 
servations. First, That in all this debate about 
the existence of a material world, it hath been 
taken for granted on both sides, that this same 
material world, if any such there be, must be the 
express image of our sensations; that we can have 
no conception of any material thing which is not 
like some sensation in our minds: and particular- 
ly, that the sensations of touch are images of ex- 
tension, hardness, figure and motion. Every 
argument brought against the existence of a 
material world, either by the Bishop of Cloyne, 
or by the author of the Treatise of Human Nature, 
supposeth this. If this is true, their arguments 
are conclusive and unanswerable: but, on the 
other hand, if it is not true, there is no shadow 
of argument left. Have those philosophers, then, 
given any solid proof of this hypothesis, upon 
which the whole weight of so strange a system 
rests? No. They have not so much as attempt- 



SECT. 7.] OF TOUCH. 1&5 

ed to do it. But, because ancient and modern 
philosophers have agreed in this opinion, they 
have taken it for granted. But let us, as be- 
comes philosophers, lay aside authority; we need 
not surely consult Aristotle or Locke, to know 
whether pain be like the point of a sword. I 
have as clear a conception of extension, hard- 
ness, and motion, as I have of the point of a 
sword; and, with some pains and practice, I can 
form as clear a notion of the other sensations of 
touch, as I have of pain. When I do so, and 
compare them together, it appears to me clear as 
day-light, that the former are not of kin to the 
latter, nor resemble them in any one feature. 
They are as unlike, yea, as certainly and mani- 
festly unlike, as pain is to the point of a sword. 
It may be true, that those sensations first intro- 
duced the material world to our acquaintance; it 
may be true, that it seldom or never appears 
without their company; but, for all that, they 
are as unlike as the passion of anger is to those 
features of the countenance which attend it. 

So that, in the sentence those philosophers 
have passed against the material world, there is 
an error personce. Their proof touches not mat- 
ter, or any of its qualities; but strikes directly 
against an idol of their own imagination, a ma- 
terial world made of ideas and sensations, which 
never had nor can have an existence. 

Secondly, The very existence of our concep- 
tions of extension, figure, and motion, since they 
are neither ideas of sensation nor reflection, 



126 OF THE HUMAN MIND. [CHAP. 5. 

overturns the whole ideal system, by which the 
material world hath been tried and comdemned: 
so that there hath been likewise in this sentence 
an error juris. 

It is a very fine and a just observation of 
Locke, That as no human art can create a single 
particle of matter, and the whole extent of our 
power over the material world, consists in com- 
pounding, combining, and disjoining the mat- 
ter made to our hands; so in the world of 
thought, the materials are all made by nature, 
and can only be variously combined and disjoined 
by us. So that it is impossible for reason to pre- 
judice, true or false philosophy, or produce one 
simple notion or conception, which is not the 
work of nature, and the result of our constitu- 
tion. The conception of extension, motion, and 
the other attributes of matter, cannot be the ef- 
fect of error or prejudice; it must be the work 
of nature. And the power or faculty, by which 
v/e acquire those conceptions, must be something 
different from any power of the human mind that 
hath been explained, since it is neither sensation 
nor reflection. 

Thus I would therefore humbly propose as an 
experimentum cruris, by which the ideal system 
must stand or fall; and it brings the matter to a 
short issue: Extension, figure, motion, may, any 
one, or all of them, be taken for the subject of 
this experiment. Either they are ideas of sensa- 
tion, or they are not. If any one of them can be 
shewn to be an idea of sensation, or to have the 



SECT. 7-] OF TOUCH. 12J 

least resemblance to any sensation, I lay my hand 
upon my mouth, and give up all pretence to re- 
concile reason to common sense in this matter, 
and must suffer the ideal scepticism to triumph. 
But if, on the other hand, they are not ideas of 
sensation nor like any sensation, then the ideal 
system is a rope of sand, and all the laboured 
arguments of the sceptical philosophy against a 
material world, and against the existence of every 
thing but impressions and ideas, proceed upon a 
false hypothesis. 

If our philosophy concerning the mind be so 
lame with regard to the origin of our notions of 
the clearest, most simple, and most familiar ob- 
jects of thought and the powers from which they 
are derived, can we expect that it should be more 
perfect in the account it gives of the origin of 
our opinions and belief? We have seen already 
some instances of its imperfection in this respect: 
and perhaps that same nature which hath given 
us the power to conceive things altogether un- 
like to any of our sensations, or to any operation 
of our minds, hath likewise provided for our be- 
lief of them, by some part of our constitution 
hitherto not explained. 

Bishop Berkeley hath proved, beyond the pos- 
sibility of reply, that we cannot by reasoning in- 
fer the existence of matter from our sensations: 
and the author of the Treatise of Human Nature 
hath proved no less clearly, that we cannot by 
reasoning infer the existence of our own or other 
minds from our sensations. But are we to admit 



128 OF THE HUMAN MIND. CHAP. 5* 

nothing but what can be proved by reasoning ? 
Then we must be sceptics indeed, and believe 
nothing at all. The author of the Treatise of 
Human Natiwe appears to me to be but a half 
sceptic. He hath not followed his principles so 
far as they lead him: but after having, with un- 
paralleled intrepidity and success, combated vul- 
gar prejudices; when he had but one blow to 
strike, his courage fails him, he fairly lays down 
his arms, and yields himself a captive to the most 
common of all vulgar prejudices, I mean the be- 
lief of the existence of his own impressions and 
ideas. 

I beg, therefore, to have the honour of making 
an addition to the sceptical system, without which, 
I conceive, it cannot hang together. I affirm, 
that the belief of the existence of impressions and 
ideas is as little supported by reason as that of 
the existence of minds and bodies. No man ever 
did, or could offer any reason for this belief. Des 
Cartes took it for granted, that he thought and 
had sensations and ideas; so have all his follow- 
ers done. Even the hero of scepticism hath yield- 
ed this point, I crave leave to say weakly and 
imprudently. I say so, because I am persuaded 
that there is no principle of his philosophy that 
obliged him to make this concession. And what 
is there in impressions and ideas so formidable, 
that this all-conquering philosophy, after tri- 
umphing over every other existence, should pay 
homage to him? Besides, the concession is dan- 
gerous: for belief is of- such a nature^ that if you 



SECT. 70 OF TOUCH. 129 

leave any root it will spread, and you may more 
easily pull it up altogether, than say, Hitherto 
shalt thou go and no farther: the existence of 
impressions and ideas I give up to thee; but see 
thou pretend to nothing more. A thorough and 
consistent sceptic will never, therefore, yield this 
point; and while he holds it, you can never oblige 
him to yield any thing else. 

To such a sceptic I have nothing to say; but 
of the semi-sceptics, I should beg leave to know, 
why they believe the existence of their impres- 
sions and ideas. The true reason I take to be, 
because they cannot help it; and the same reason 
will lead them to believe many other things. 

All reasoning must be from first principles; 
and for first principles no other reason can be 
given but this, that, by the constitution of our 
nature, we are under a necessity of assenting to 
them. Such principles are parts of our constitu- 
tion, no less than the power of thinking: reason 
can neither make nor destroy them; nor can it 
do any thing without them: it is like a telescope, 
which may help a man to see farther, who hath 
eyes; but without eyes, a telescope shews no- 
thing at all. A mathematician cannot prove the 
truth of his axioms, nor can he prove any thing, 
unless he takes them for granted. We cannot 
prove the existence of our minds, nor even of our 
thoughts and sensations. A historian, or a wit- 
ness, can prove nothing, unless it is taken for 
granted that the memory and senses may be 
trusted. A natural philosopher can prove no- 



130 OF THE HUMAN MIND* [CHAP. 5. 

thing, unless it is taken for granted that the 
course of nature is steady and uniform. 

How or when I got such first principles, upon 
which I build all my reasoning, I know not; for 
I had them before I can remember: but I am sure 
they are parts of my constitution, and that I cannot 
throw them off. That our thoughts and sensa- 
tions must have a subject, which we call our self > 
is not therefore an opinion got by reasoning, but 
a natural principle. That our sensations of touch 
indicates something external, extended, figured, 
hard or soft, is not a deduction of reason, but a 
natural principle. The belief of it, and the very 
conception of it, are equally parts of our consti- 
tution. If we are deceived in it, we are deceiv- 
ed by Him that made us, and there is no reme- 
dy. 

I do not mean to affirm, that the sensations of 
touch do from the very first suggest the same 
notions of body and its qualities which they do 
when we are grown up. Perhaps nature is frugal 
in this, as in her other operations. The passion 
of love, with all its concomitant sentiments and 
desires, is naturally suggested by the perception 
of beauty in the other sex. Yet the same per- 
ception does not suggest the tender passion, till 
a certain period of life. A blow given to an in- 
fant, raises grief and lamentation; but when he 
grows up, it as naturaly stirs resentment, and 
prompts him to resistance. Perhaps a child in 
the womb, or for some short period of its exist- 
ence, is merely a sentient being : the faculties. 



SECT. 7.] OF TOUCH. 131 

by which it perceives an external world, by which 
it reflects on its own thoughts and existence, 
and relation to other things, as well as its reason- 
ing and moral faculties, unfold themselves by de- 
grees; so that it is inspired with the various 
principles of common sense, as with the passions 
of love and resentment, when it has occasion for 
them. 



SECT. VIII. 

Of the systems of philosophers concerning the senses. 

All the systems of philosophers about our senses 
and their objects have split upon this rock, of 
not distinguishing properly sensations, which can 
have no existence but when they are felt, from 
the things suggested by them. Aristotle, with 
as distinguishing a head as ever applied to philo- 
sophical disquisitions, confounds these two; and 
makes every sensation to be the form, without 
the matter, of the thing perceived by it: As the 
impression of a seal upon wax has the form of 
the seal, but nothing of the matter of it; so he 
conceived our sensations to be impressions upon 
the mind, which bear the image, likeness, or form 
of the external thing perceived, without the mat- 
ter of it. Colour, sound, and smell, as well as ex- 
tension, figure, and hardness, are, according to 
him, various forms of matter: our sensations are 

i2 



132 OF THE HUMAN MIND. [CHAP. 5. 

the same forms imprinted on the mind, and per- 
ceived in its own intellect. It is evident from 
this, that Aristotle made no distinction be- 
tween primary and secondary qualities of bodies, 
although that distinction was made by Demo- 
critus, Epicurus, and others of the ancients. 

Des Cartes, Malebranche, and Locke, re- 
vived the distinction between primary and se- 
condary qualities. But they make the secondary 
qualities mere sensations, and the primary ones 
resemblances of our sensations. They maintain- 
ed, that colour, sound, and heat, are not any 
thing in bodies, but sensations of the mind: at 
the same time, they acknowledged some particu- 
lar texture or modification of the body, to be the 
cause or occasion of those sensations; but to this 
modification they gave no name. Whereas, by 
the vulgar, the names of colour, heat, and sound, 
are but rarely applied to the sensations, and most 
commonly to those unknown causes of them; as 
hath been already explained. The constitution 
of our nature leads us rather to attend to the 
things signified by the sensation, than to the sens- 
ation itself, and to give a name to the former 
rather than to the latter. Thus we see, that with 
regard to secondary qualities, these philosophers 
thought with the vulgar, and with common sense. 
Their paradoxes were only an abuse of words. 
For when they maintain, as an important modern 
discovery, that there is no heat in the fire, they 
mean no more, than that the fire does not feel 
lieat, which e\ery one knew before. 



SECT. 12.] OP TOUCH. 13$ 

With regard to primary qualities, these philo- 
sophers erred most grossly: they indeed believed 
the existence of those qualities; but they did not 
at all attend to the sensations that suggest them, 
which have no names, having been as little con- 
sidered as if they had no existence. They were 
aware, that figure, extension and hardness, are 
perceived by means of sensations of touch: whence 
they rashly concluded, that these sensations must 
be images and resemblances of figure, extension 
and hardness. 

The received hypothesis of ideas naturally led 
them to this conclusion; and indeed cannot exist 
with any other; for, according to that hypothe- 
sis, external things must be perceived by means 
of images of them in the mind; and what can 
those images of external things in the mind be, 
but the sensations by which we perceive them? 

This, however, was to draw a conclusion from 
a hypothesis against fact. We need not have re- 
course to any hypothesis to know what our sen- 
sations are, or what they are like. By a proper 
degree of reflection and attention, we may under- 
stand them perfectly, and be as certain that they 
are not like any quality of body, as we can be, 
that the toothach is not like a triangle. How a 
sensation should instantly make us conceive and 
believe the existence of an external thing alto- 
gether unlike to it, I do not pretend to know; 
and when I say that the one suggests the other, 
I mean not to explain the manner of their con- 
nection, but to express a fact, which every one 

i 3 



134 OF THE HUMAN MIND. [CHAP. 5. 

may be conscious of; namely, that, by a law of 
our nature, such a conception and belief con- 
stantly and immediately follow the sensation. 

Bishop Berkeley gave new light to this sub- 
ject, by shewing, that the qualities of an inani- 
mate thing, such as matter is conceived to be, 
cannot resemble any sensation; that it is impos- 
sible to conceive any thing like the sensations of 
our minds, but the sensations of other minds. 
Every one that attends properly to these sensa- 
tions must assent to this; yet it hath escaped all 
the philosophers that came before Berkeley: it 
had escaped even the ingenious Locke, who had 
so much practised reflection on the operations of 
his own mind. So difficult is it to attend proper- 
ly even to our own feelings. They are so accus- 
tomed to pass through the mind unobserved, and 
instantly to make way for that which nature in- 
tended them to signify, that it is extremely diffi- 
cult to stop, and survey them; and when we think 
we have acquired this power, perhaps the mind 
still fluctuates between the sensation and its as- 
sociated quality, so that they mix together, and 
present something to the imagination that is com- 
pounded of both, This in a globe or cylinder, 
whose opposite sides are quite unlike in colour, 
if you turn it slowly, the colours are perfectly 
distinguishable, and their dissimilitude is mani- 
fest; but if it is turned fast, they lose their dis- 
tinction, and seem to be of one and the same co- 
lour. 

No succession can be more quick, than that of* 



SECT. 8.] OF TOUCH. 135 

tangible qualities to the sensations with which na- 
ture has associated them : But when one has once 
acquired the art of making them separate and 
distinct objects of thought, he will then clearly 
perceive, that the maxim of Bishop Berkeley 
above mentioned, is self-evident; and that the 
features of the face are no more unlike to a pas- 
sion of the mind which they indicate, than the 
sensations of touch are to the primary qualities of 
body. 

But let us observe what use the Bishop makes 
of this important discovery: Why, he concludes, 
that we can have no conception of an inanimate 
substance, such as matter is conceived to be, or of 
any of its qualities; and that there is the strongest 
ground to believe that there is no existence in 
nature but minds, sensations, and ideas: If there 
is any other kind of existence, it must be what 
we neither have nor can have any conception of. 
But how does this follow? Why thus: We can 
have no conception of any thing but what resem- 
bles some sensation or idea in our minds; but the 
sensations and ideas in our minds can resemble 
nothing but the sensations and ideas in other 
minds; therefore, the conclusion is evident. 
This argument, we see, leans upon two proposi- 
tions. The last of them the ingenious author 
hath indeed made evident to all that understand 
his reasoning, and can attend to their own sensa^ 
tions: but the first proposition he never attempts 
to prove: it is taken from the doctrine of ideas,. 
which hath been so universally received by 



136 OF THE HUMAN MIND. [CHAP. 6. 

philosophers, that it was thought to need no 
proof. 

We may here again observe, that this acute 
writer argues from a hypothesis against fact, and 
against the common sense of mankind. That we 
can have no conception of any thing, unless there 
is some impression, sensation, or idea, in our 
minds which resembles it, is indeed an opinion 
which hath been very generally received among 
philosophers; but it is neither self-evident, nor 
hath it been clearly proved: and therefore it had 
been more reasonable to call in question this 
doctrine of philosophers, than to discard the ma- 
terial world, and by that means expose philoso- 
phy to the ridicule of all men who will not offer 
up common sense as a sacrifice to metaphysics. 

We ought, however, to do this justice both to 
the Bishop of Cloyne, and to the author of the 
Treatise of Human Nature^ to acknowledge, that 
their conclusions are justly drawn from the doc- 
trine of ideas, which has been so universally re- 
ceived. On the other hand, from the character 
of Bishop Berkeley, and of his predecessors Des 
Cartes, Locke, and Malebranche, we may 
venture to say, that if they had seen all the con- 
sequences of this doctrine as clearly as the au- 
thor before mentioned did, they would have sus- 
pected it vehemently, and examined it more care- 
fully than they appear to have done. 

The theory of ideas, like the Trojan horse, had 
a specious appearance both of jinnocence and 
beauty j but if those philosophers had known that 



SECT. 8.3 OF TOUCH. 137 

it carried in its belly death and destruction to all 
science and common sense, they would not have 
broken down their walls to give it admittance. 

That we have clear and distinct conceptions of 
extension, figure, motion, and other attributes of 
body, which are neither sensations, nor like any 
sensation, is a fact of which we may be as certain, 
as that we have sensations. And that all man- 
kind have a fixed belief of an external material 
world, a belief which is neither got by reasoning 
nor education, and a belief which we cannot shake 
off, even when we seem to have strong arguments 
against it, and no shadow of argument for it, is 
likewise a fact, for which we have all the evidence 
that the nature of the thing admits. These facts 
are phenomena of human nature, from which we 
may justly argue against any hypothesis, however 
generally received. But to argue from a hypo- 
thesis against facts, is contrary to the rules of 
true philosophy. 



138 OF THE HUMAN MIND. [CHAP. G. 

CHAP. VI. 

OF SEEING. 

— — — » ■ *" 'H ■ »— —— — »WP— — — 

SECT. I. 

T/^ excellency and dignity of this Faculty. 

1 he advances made in the knowledge of optics 
in the last age, and in the present, and chiefly 
the discoveries of Sir Isaac Newton, do honour 
not to philosophy only, but to human nature* 
Such discoveries ought for ever to put to shame 
the ignoble attempts of our modern sceptics to 
depreciate the human understanding, and to di- 
spirit men in the search of truth, by representing 
the human faculties as fit for nothing, but to lead 
us into absurdities and contradictions. 

Of the faculties called the five senses, sight is 
without doubt the noblest. The rays of light 
which minister to this sense, and of which, with- 
out it, we could never have had the least con- 
ception, are the most wonderful and astonishing 
part of the inanimate creation. We must be sa- 
tisfied of this, if we consider their extreme mi- 
nuteness, their inconceivable velocity, the regular 
variety of colours which they exhibit, the invari- 



SECT. 1.] OF SEEING. 139 

able laws according to which they are acted upon 
by other bodies, in their reflections, inflections, 
and refractions, without the least change of their 
original properties, and the facility with which 
they pervade bodies of great density, and of 
the closest texture, without resistance, without 
crowding or disturbing one another, without 
giving the least sensible impulse to the lightest 
bodies. 

The structure of the eye, and of all its appur- 
tenances, the admirable contrivance of nature 
for performing all its various external and inter- 
nal motions, and the variety in the eyes of differ- 
ent animals, suited to their several natures and 
ways of life, clearly demonstrate this organ to be 
a masterpiece of Nature's work. And he must 
be very ignorant of what hath been discovered 
about it, or have a very strange cast of under- 
standing, who can seriously doubt, whether or 
not the rays of light and the eye were made for 
one another, with consummate wisdom, and per- 
fect skill in optics. 

If we shall suppose an order of beings, endued 
with every human faculty but that of sight, how 
incredible would it appear to such beings accus- 
tomed only to the slow information of touch, that, 
by the addition of an organ, consisting of a ball 
and socket of an inch diameter, they might be 
enabled in an instant of time, without changing 
their place, to perceive the disposition of a whole 
army, or the order of a battle, the figure of a 
magnificent palace, or all the variety of a land- 



140 OF THE HUMAN MIND. [CHAP. 6. 

scape? If a man were by feeling to find out the 
figure of the peak of Teneriffe, or even of St. 
Peter's Church at Rome, it would be the work of 
a lifetime. 

It would appear still more incredible to such 
beings as we have supposed, if they were inform- 
ed of the discoveries which may be made by this 
little organ in things far beyond the reach of any 
other sense: That by means of it we can find 
our way in the pathless ocean ; that we can tra- 
verse the globe of the earth, determine its figure 
and dimensions, and delineate every region of it; 
Yea, that we can measure the planetary orbs, 
and make discoveries in the sphere of the fixed 
stars. 

Would it not appear still more astonishing to 
such beings, if they should be farther informed, 
That, by means of this same organ, we can per- 
ceive the tempers and dispositions, the passions 
and affections of our fellow-creatures, even when 
they want most to conceal them? That when the 
tongue is taught most artfully to lie and dissem- 
ble, the hypocrisy should appear in the counte- 
nance to a discerning eye? And that by this or- 
gan we can often perceive what is straight and 
what is crooked in the mind as well as in the 
body? How many mysterious things must a blind 
man believe, if he will give credit to the relations 
of those that see? Surely he needs as strong a 
faith as is required of a good Christian. 

It is not therefore without reason, that the 
faculty of seeing is looked upon, not only as more 



SECT. 2.] OF SEEING. Ill 

noble than the other senses, but as having some- 
thing in it of a nature superior to sensation. The 
evidence of reason is called seeing, not feeling, 
smelling, or tasting. Yea, we are wont to express 
the manner of the divine knowledge by seeing, as 
that kind of knowledge which is most perfect in 
us* 



SECT. II. 



Sight discovers almost nothing which the blind may^ 
not comprehend. The reason of tJiis. 

Notwithstanding what hath been said of the 
dignity and superior nature of this faculty, it is 
w T orthy of our observation that there is very lit- 
tle of the knowledge acquired by sight, that may 
not be communicated to a man born blind. One 
who never saw the light, may be learned and 
knowing in every science, even in optics; and 
may make discoveries in every branch of philo- 
sophy. He may understand as much as another 
man, not only of the order, distances, and mo- 
tions, of the heavenly bodies; but of the nature 
of light, and of the laws of the reflection and re- 
fraction of its rays. He may understand distinct- 
ly, how those laws produce the phenomena of the 
rainbow, the prism, the camera obscura, and the 
magic lanthorn, and all the powers of the micro- 



142 OF THE HUMAN MIND. [CHAP. 6. 

scope and telescope. This is a fact sufficiently 
attested by experience. 

In order to perceive the reason of it, we must 
distinguish the appearance that objects make to 
the eye, from the things suggested by that ap- 
pearance; and again, in the visible appearance of 
objects, we must distinguish the appearance of 
colour from the appearance of extension, figure, 
and motion. First, then, as to the visible appear- 
ance of the figure, and motion, and extension of 
bodies, I conceive that a man born blind may have 
a distinct notion, if not of the very things, at least 
of something extremely like to them. May not a 
blind man be made to conceive, that a body mov- 
ing directly from the eye, or directly towards it, 
may appear to be at rest? and that the same mo- 
tion may appear quicker or slower, according as it 
is nearer to the eye or farther off, more direct or 
more oblique? May he not be made to conceive 
that a plain surface, in a certain position, may- 
appear as a straight line, and vary its visible fi- 
gure, as its position, or the position of the eye, 
is varied? That a circle seen obliquely will 
appear an ellipse; and a square, a rhombus or 
an oblong rectangle? Dr. Saunderson under- 
stood the projection of the sphere, and the com- 
mon rules of perspective; and if he did he 
must have understood all that I have mention- 
ed. If there were any doubt of Dr. Saunder- 
son's understanding these things, I could men- 
tion my having heard him say in conversa- 
tion, that he found great difficulty in under- 



SECT. 2.] OF SEEING. 143 

standing Dr. Halley's demonstration of that 
proposition, That the angles made by the circles 
of the sphere, are equal to the angles made 
by their representatives in the stereo-graphic pro- 
jection: But, said he, when I laid aside that de- 
monstration, and considered the proposition in 
my own way, I saw clearly, that it must be true. 
Another gentleman, of undoubted credit and 
judgment in these matters, who had part in this 
conversation, remembers it distinctly. 

As to the appearance of colour, a blind man 
must be more at a loss; because he hath no per- 
ception that resembles it. Yet he may, by a kind 
of analogy, in part supply this defect. To those 
who see, a scarlet colour signifies an unknown 
quality in bodies, that makes to the eye an ap- 
pearance, which they are well acquainted with, 
and have often observed: to a blind man, it sig- 
nifies an unknown quality that makes to the eye 
an appearance which he is unacquainted with. 
But he can conceive the eye to be variously af- 
fected by different colours, as the nose is by dif- 
ferent smells, or the ear by different sounds. 
Thus he can conceive scarlet, to differ from blue, 
as the sound of a trumpet does from that of a 
drum; or as the smell of an orange differs from 
that of an apple. It is impossible to know whether 
a scarlet colour has the same appearance to me 
which it hath to another man; and if the appear- 
ances of it to different persons differed as much 
as colour does from sound, they might never be 
able to discover this difference. Hence it ap- 



144 OF THE HUMAN MIND. f CHAP. 6. 

pears obvious, that a blind man might talk long 
about colours distinctly and pertinently: and if 
you were to examine him in the dark about th^ 
nature, composition, and beauty of them, he 
might be able to answer, so as not to betray his 
defect. 

We have seen how far a blind man may go in 
the knowledge of the appearances which things 
make to the eye. As to the things which are 
suggested by them, ■ or inferred from them, al- 
though he could never discover them of himself, 
yet he may understand them perfectly by the in- 
formation of others. And every thing of this 
kind that enters into our minds by the eye, may 
enter into his by the ear. Thus, for instance, he 
could never, if left to the direction of his own 
faculties, have dreamed of any such thing as light; 
but he can be informed of every thing we know 
about it. He can conceive, as distinctly as we, 
the minuteness and velocity of its rays, their va- 
rious degrees of refrangibility and reflexibility, 
and all the magical powers and virtues of that 
wonderful element. He could never of himself 
have found out, that there are such bodies, as the 
sun, moon, and stars; but he may be informed of 
all the noble discoveries of astronomers about 
their motions, and the laws of nature by which 
they are regulated. Thus it appears, that there 
is very little knowledge got by the eye, which 
may not be communicated by language to those 
who have no eyes. $ 

If we should suppose, that it were as uncom- 



SECT. 2.] OF SEEING. 145 

mon for men to see, as it is to be born blind ; 
would not the few who had this rare gift, appear 
as prophets and inspired teachers to the many? 
We conceive inspiration to give a man no new 
faculty, but to communicate to him in a new 
way, and by extraordinary means, what the facul- 
ties common to mankind can apprehend, and what 
he can communicate to others by ordinary means. 
On the supposition we have made, sight would 
appear to the blind very similar to this; for the 
few who had this gift would communicate the 
knowledge acquired by it to those who had it not. 
They could not indeed convey to the blind, any 
distinct notion of the manner in which they 
acquired this knowledge. A ball and socket 
would seem, to a blind man, in this case, as im- 
proper an instrument for acquiring such a variety 
and extent of knowledge, as a dream or a vision. 
The manner in which a man who sees, discerns 
so many things by means of the eye, is as unin- 
telligible to the blind, as the manner in which a 
man may be inspired with knowledge by the Al- 
mighty, is to us. Ought the blind man, there- 
fore, without examination, to treat all pretences 
to the gift of seeing as imposture? Might he not, 
if he were candid and tractable, find reasonable 
evidence of the reality of this gift in others, and 
draw great advantages from it to himself? 

The distinction w 7 e have made between the 
visible appearances of the objects of sight, and 
things suggested by them, is necessary to give us 
a just notion of the intention of nature in giving 

K 



146 of thb; human mind. [chap. 6, 

us eyes. If we attend duly to the operation of 
our mind in the use of this faculty, we shall per- 
ceive, that the visible appearance of objects is 
hardly ever regarded by us. It is not at all made 
an object of thought or reflection, but serves only 
as a sign to introduce to the mind something 
else, which may be distinctly conceived by those 
who never saw. 

Thus, the visible appearance of things in my 
room varies almost every hour, according as the 
day is clear or cloudy, as the sun is in the east, 
or south, or west, and as my eye is in one part 
of the room or in another: but I never think of 
these variations, otherwise than as signs of morn- 
ing, noon, or night, of a clear or cloudy sky. A 
book or a chair has a different appearance to the 
eye, in every different distance or position ; yet 
we conceive it to be still the same; and, over- 
looking the appearance, we immediately conceive 
the real figure, distance, and position of the body, 
of which its visible or perspective appearance is 
a sign and indication. 

When I see a man at the distance of ten yards, 
and afterwards see him at the distance of a hun- 
dred yards, his visible appearance in its length, 
breadth, and all its linear proportions, is ten times 
less in the last case than it is in the first: yet I 
do not conceive him one inch diminished by this 
diminution of his visible figure. Nay, I do not 
in the least attend to this diminution, even when 
I draw from it the conclusion of his being at a 
greater distance. For such is the subtilty of the 



SECT. 2.] OF SEEING. 117 

mind's operation in this case, that we draw the 
conclusion, without perceiving that ever the pre- 
mises entered into the mind. A thousand such 
instances might be produced, in order to shew 
that the visible appearances of objects are intend- 
ed by nature only as signs or indications; and 
that the mind passes instantly to the things sig- 
nified, without making the least reflection upon 
the sign, or even perceiving that there is any 
such thing. It is in a way somewhat similar, 
that the sounds of a language, after it is become 
familiar, are overlooked, and we attend only to 
the things signified by them. 

It is therefore a just and important observation 
of the Bishop of CJoyne, That the visible ap- 
pearance of objects is a kind of language used by 
nature, to inform us of their distance, magni- 
tude, and figure. And this observation hath 
been very happily applied by that ingenious writ- 
er, to the solution of some phenomena in optics, 
which hath before perplexed the greatest masters 
in that science. The same observation is fur- 
ther improved by the judicious Dr. Smith, in his 
Optics, for explaining the apparent figure of the 
heavens,, and the apparent distances and mag- 
nitudes of objects seen with glasses, or by the 
naked eye. 

Avoiding as much as possible the repetition of 
what hath been said by these excellent writers, 
we shall avail ourselves of the distinction between 
the signs that nature useth in this visual language, 
and the tilings signified by them; and iri what 

k % 



148 OF THE HUMAN MIND, [CHAP. 6. 

remains to be said of sight, shall first make some 
observations upon the sight. 



SECT. III. 

Of the visible appearances of objects. 

In this section we must speak of things which 
are never made the object of reflection, though 
almost every moment presented to the mind. 
Nature intended them only for signs; and in the 
whole course of life they are put to no other use* 
The mind has acquired a confirmed and inveterate 
habit of inattention to them ; for they no sooner 
appear, than quick as lightning the thing signified 
succeeds, and engrosses all our regard. They 
have no name in language; and although we are 
conscious of them when they pass through the 
mind, yet their passage is so quick, and so fami- 
liar, that it is absolutely unheeded; nor do they 
leave any footsteps of themselves, either in the 
memory or imagination. That this is the case 
with regard to the sensations of touch, hath been 
shown in the last chapter; and it holds no less 
with regard to the visible appearances of objects. 
I cannot therefore entertain the hope of being 
intelligible to those readers who have not, by, 
pains and practice, acquired the habit of distin- 
guishing the appearance of objects to the eye, 
from the judgment which we form by sight, of 



SECT. 3.] OF SEEING. 149 

their colour, distance, magnitude, and figure. 
The only profession in life wherein it is neces- 
sary to make this distinction, is that of painting. 
The painter hath occasion for an abstraction, 
with regard to visible objects, somewhat similar 
to that which we here require: and this indeed 
is the most difficult part of his art. For it is evi- 
dent, that if he could fix in his imagination the 
visible appearance of objects, without confound- 
ing it with the things signified by that appear- 
ance, it would be as easy for him to paint from 
the life, and to give every figure its proper shad- 
ing and relief, and its perspective proportions, 
as it is to paint from a copy. Perspective, shad- 
ing, giving relief, and colouring, are nothing 
else but copying the appearance which things 
make to the eye. We may therefore borrow some 
light on the subject of visible appearance from 
this art. 

Let one look upon any familiar object, such as 
a book, at different distances and different posi- 
tions'; is he not able to affirm, upon the testimony 
of his sight, that it is the came book, the same 
object, whether seen at the distance of one foot 
or of ten, whether in one position or another; 
that the colour is the same, the dimensions the 
same, and the figure the same, as far as the eye 
can judge? This surely must be acknowledged. 
The same individual object is presented to the 
mind, ouly placed at different distances, and in 
different positions. Let me ask, in the next 
place, Whether this object has the same appear- 

k3 



150 OF THE HUMAN MIND. [CHAP. 6. 

ance to the eye in these different distances? In- 
fallibly it hath not. For, 

First, However certain our judgment may be, 
that the colour is the same, it is as certain that it 
hath not the same appearance at different dis- 
tances. There is a certain degradation of the 
colour, and a certain confusion and indistinctness 
of the minute parts, which is the natural conse- 
quence of the removal of the object to a greater 
distance. Those that are not painters, or critics 
in painting, overlook this; and cannot easily be 
persuaded, that the colour of the same object hath 
a different appearance at the distance of one foot 
and. of ten, in the shade and in the light. But 
the masters in painting know how, by the degra- 
dation of the colour, and the confusion of the mi- 
nute parts, figures, which are upon the same can- 
vas, and at the same distance from the eye, may 
be made to represent objects which are at the most 
unequal distances. They know how to make the 
objects appear to be of the same colour, by mak- 
ing their pictures really of different colours, ac- 
cording to their distances or shades. 

Secondly, Every one who is acquainted with 
the rules of perspective, knows that the appear- 
ance of the figure of the books must vary in every 
different position ; yet if you ask a man that has 
no notion of perspective, whether the figure of it 
does not appear to his eye to be the same in all 
its different positions? he can with a good con- 
science affirm, that it does. He hath learned to 
make allowance for the variety of visible figure 



SECT. 3.] OF SEEING. 151 

arising from the difference of position, and to 
draw the proper conclusions from it. But he 
draws these conclusions so readily and habitually, 
as to lose sight of the premises; and, therefore, 
where he hath made the same conclusions, he con- 
ceives the visible appearance must have been the 
same. 

Thirdly, Let us consider the apparent magni- 
tude or dimensions of the book. Whether I view 
it at a distance of one foot or of ten feet, it 
seems to be about seven inches long, five broad, 
and one thick. I can judge of these dimensions 
very nearly by the eye, and I judge them to be 
the same at both distances. But yet it is certain 
that at the distance of one foot, its visible length 
and breadth is about ten times as great as at the 
distance of ten feet; and consequently its surface 
is about a hundred times as great. This great 
change of apparent magnitude is altogether over- 
looked, and every man is apt to imagine, that it 
appears to the eye of the same size at both dis- 
tances. Further, when I look at the book, it 
seems plainly to have three dimensions, of length, 
breadth, and thickness: but it is certain that the 
visible appearance hath no more, than two, and 
can be exactly represented upon a canvas which 
hath only length and breadth. 

In the last place, Does not every man, by sight, 
perceive the distance of the book from his eye? 
Can he not affirm with certainty, that in one case 
it is not above one foot distant, that in another it 
is ten? Nevertheless it appears certain, that dis- 



152 OF THE HUMAN MIND. [CHAP. 6. 

tance from the eye, is no immediate object of 
sight. There are certain things in the visible 
appearance, which are signs of distance from the 
eye, and from which as we shall afterwards show, 
we learn by experience to judge of that distance 
within certain limits ; but it seems beyond doubt, 
that a man born blind, and suddenly made to see, 
could form no judgment at first of the distance 
of the objects which he saw. The young man 
couched by Cheselden, thought, at first, that 
every thing he saw touched his eye, and learned 
only by experience to judge of the distance of 
visible objects, 

I have entered into this long detail, in order 
to show, that the visible appearance of an object 
is extremely different from the notion of it which 
experience teaches us to form by sight; and to 
enable the reader to attend to the visible appear- 
ance of colour, figure, and extension, in visible 
things, which is no common object of thought, 
but must be carefully attended to by those who 
would enter into the philosophy of this sense, or 
would comprehend what shall be said upon it. To 
a man newly made to see, the visible appearance 
of objects would be the same as to us; but he 
would see nothing at all of their real dimensions, 
as we do. He could form no conjecture, by 
means of his sight only, how many inches or feet 
they were in length, breadth, or thickness. He 
could perceive little or nothing of their real figure; 
nor could he discern that this was a cube, that a 
sphere: that this was a cone, and that a cylinder. 



SECT. 4.] OF SEEING. 153 

His eye could not inform him, that this object 
was near, and that more remote. The habit 
of a man or of a woman, which appeared to us of 
one uniform colour variously folded and shaded, 
would present to his eye neither fold nor shade, 
but variety of colour. In a word, his eyes, though 
ever so perfect, would at first give him almost 
no information of things without him. They 
would indeed present the same appearances to 
him as they do to us, and speak the same lan- 
guage ; but to him it is an unknown language, and 
therefore he would attend only to the signs, with- 
out knowing the signification of them: whereas 
to us it is a language perfectly familiar; and 
therefore we take no notice of the signs, but at- 
tend only to the thing signified by them. 



SECT. IV. 



That colour is a quality of bodies, not a sensation 
of the mind. 

By colour, all men, who have not been tutored 
by modern philosophy, understand, not a sensa- 
tion of the mind, which can have no existence 
when it is not perceived, but a quality or modi- 
fication of bodies, which continues to be the same, 
whether it is seen or not. The scarlet-rose, which 
is before me, is still a scarlet-rose when I shut my 
eyes, and was so at midnight when no eye saw it. 



15 4f OF THE HUMAN MIND. [CHAP. 6* 

The colour remains when the appearance ceases: it 
remains the same when the appearance changes. 
For when I view this scarlet-rose through a pair 
of green spectacles, the appearance is changed, 
but I do not conceive the colour of the rose 
changed. To a person in the jaundice, it has 
still another appearance; but he is easily con- 
vinced, that the change is in his eye, and not in 
the colour of the object. Every different degree 
of light makes it have a different appearance, and 
total darkness takes away all appearance, but 
makes not the least change in the colour of the 
body. We may, by a variety of optical experi- 
ments, change the appearance of figure and mag- 
nitude in a body, as well as that of colour; we 
may make one body appear to be ten. But all 
men believe, that as a multiplying glass does not 
really produce ten guineas out of one, nor a mi- 
croscope turn a guinea into a ten pound piece; 
so neither does a coloured glass change the real 
colour of the object seen through it, when it 
changes the appearance of that colour. 

The common language of mankind shows evi- 
dently, that we ought to distinguish between the 
colour of a body, which is conceived to be a fix- 
ed and permanent quality in the body, and the 
appearance of that colour to the eye, which may 
be varied a thousand ways, by a variation of the 
light, of the medium, or of the eye itself. The 
permanent colour of the body is the cause, which, 
by the mediation of various kinds or degrees of 
light, and of various transparent bodies interpos- 



SECT. 4.] OF SEEING. 155 

ed, produces all this variety of appearances. 
When a coloured body is presented, there is a 
certain apparition to the eye, or to the mind, 
which we have called the appearance of colour. 
Mr. Locke calls it an idea; and indeed it may 
be called so with the greatest propriety. This 
idea can have no existence but when it is per- 
ceived. It is a kind of thought, and can only be 
the act of a precipient or thinking being. By 
the constitution of our nature, we are led to con- 
ceive this idea as a sign of something external, 
and are impatient till we learn its meaning. A 
thousand experiments for this purpose are made 
every day by children, even before they come to 
the use of reason. They look at things, they 
handle them, they put them in various positions, 
at different distances, and in different lights. — 
The ideas of sight, by these means, come to be 
associated with, and readily to suggest, things 
external, and altogether unlike them. In parti- 
cular, that idea which we have called the appear- 
ance of colour, suggests the conception and belief 
of some unknown quality in the body, which oc- 
casions the idea; and it is to this quality, and 
not to the idea, that we give the name of colour. 
The various colours, although in their nature 
equally unknown, are easily distinguished when 
we think or speak of them, by being associated 
with the ideas which they excite. In like man- 
ner, gravity, magnetism, and electricity, although 
all unknown qualities, are distinguished by their 
different effects. As we grow up, the mind ac- 



156 OF THE HUMAN MIND. [CHAP. 6. 

quires a habit of passing so rapidly from the ideas 
of sight to the external things suggested by them, 
that the ideas are not in the least attended to, 
nor have they names given them in common lan- 



guage. 



When we think or speak of any particular co- 
lour, however simple the notion may seem to be 
which is presented to the imagination, it is really 
in some sort compounded. It involves an un- 
known cause, and a known effect. The name of 
colour belongs indeed to the cause only, and not to 
the effect. But as the cause is unknown, we can 
form no distinct conception of it, but by its re- 
lation to the known effect. And therefore, both 
go together in the imagination, and are so closely 
united, that they are mistaken for one simple ob- 
ject of thought. When I would conceive those 
colours of bodies which we call scarlet and blue; 
if I conceived them only as unkown qualities, I 
could perceive no distinction between the one 
and the other. I must therefore, for the sake of 
distinction, join to each of them, in my imagina- 
tion, some effect or some relation that is peculiar. 
And the most obvious distinction is, the appear- 
ance which one and the other makes to the eye. 
Hence the appearance is, in the imagination, so 
closely united with the quality called a scarlet- 
colour, that they are apt to be mistaken for one 
and the same thing, although they are in reality 
so different and so unlike, that one is an idea in 
the mind, the other is a quality of body. 

I conclude, then, that colour is not a sensation, 



SECT. 5.] OF SEEING. 157 

but a secondary quality of bodies, in the sense 
we have already explained; that it is a certain 
power or virtue in bodies, that in fair daylight 
exhibits to the eye an appearance, which is very 
familiar to us, although it hath no name. Colour- 
differs from other secondary qualities, in this, 
that whereas the name of the quality is sometimes 
given to the sensation which indicates it, and is 
occasioned by it, we never, as far as I can judge, 
give the name of colour to the sensation, but to 
the quality only. Perhaps the reason of this may 
be, that the appearances of the same colour are 
so various and changeable, according to the dif- 
ferent modifications of the light, of the medium, 
and of the eye, that language could not afford 
names for them. And indeed they are so little 
interesting, that they are never attended to, but 
serve only as signs to introduce the things signi- 
fied by them. Nor ought it to appear incredible, 
that appearances so frequent and so familiar 
should have no names, nor be made objects of 
thought; since we have before shown, that this 
is true of many sensations of touch, which are no 
less frequent, nor less familiar. 



158 €)F THE HUMAN BUND. [CHAP. 6, 

SECT. V. 

An inference from the preceding. 

From what hath been said about colour, we may 
infer two things. The first is, that one of the 
most remarkable paradoxes of modern philoso- 
phy, which hath been universally esteemed as a 
great discovery, is, in reality, when examined to 
the bottom, nothing else but an abuse of words. 
The paradox I mean is, That colour is not a 
quality of bodies, but only an idea in the mind. 
We have shown, that the word colour, as used by 
the vulgar, cannot signify an idea in the mind, 
but a permanent quality of body. We have shown 
that there is really a permanent quality of body, 
to which the common use of this word exactly 
agrees. Can any stronger proof be desired, that 
this quality is that to which the vulgar give the 
name of colour? If it should be said, that this 
quality, to which we give the name of colour, is 
unknown to the vulgar, and therefore can have 
no name among them; I answer, it is indeed 
known only by its effects; that is by its exciting 
a certain idea in us : but are there not numberless 
qualities of bodies, which are known only by their 
effects, to which, notwithstanding, we find it ne- 
cessary to give names? Medicine alone might 
furnish us with a hundred instances of this kind. 
Do not the words astringent, narcotic, eflispaslic y 



SECT. 5.] OF SEEING'. 159 

caustic, and innumerable others, signify qualities 
of bodies, which are known only by their effects 
upon animal bodies? Why then should not the 
vulgar give a name to a quality, whose effects 
are every moment perceived by their eyes? We 
have all the reason, therefore, that the nature of 
the thing admits, to think that the vulgar apply 
the name of colour to that quality of bodies, 
which excites in us what the philosophers call the 
idea of colour. And that there is such a quality 
in bodies, all philosophers allow, who allow that 
there is any such thing as body. Philosophers 
have thought fit to leave that quality of bodies, 
w r hich the vulgar call colour, without a name, 
and to give the name of colour to the idea or ap- 
pearance, to which, as we have shown, the vulgar 
give no name, because they never make it an 
object of thought or reflection. Hence it appears 
that when philosophers affirm that colour is not 
in bodies, but in the mind; and the vulgar affirm, 
that colour is not in the mind, but is a quality of 
bodies, there is no difference between them about 
things, but only about the meaning of a word. 

The vulgar have undoubted right to give 
names to things which they are daily conversant 
about; and philosophers seem justly chargeable 
with an abuse of language, when they change the 
meaning of a common word, without giving warn- 
ing. 

If it is a good rule, to think with philosophers 
and speak with the vulgar, it must be right to 
speak with the vulgar, when we think with them, 



ICO OF THE HUMAN MIND. [CHAP. 6. 

and not to shock them by philosophical paradoxes, 
which, when put into common language, express 
only the common sense of mankind. 

If you ask a man, that is no philosopher, what 
colour is? or, what makes one body appear white, 
another scarlet? He cannot tell. He leaves that 
inquiry to philosophers, and can embrace any 
hypothesis about it, except that of our modern 
philosophers, who affirm that colour is not in 
body, but only in the mind. 

Nothing appears more shocking to his appre- 
hension, than that visible objects should have no 
colour, and that colour should be in that which 
he conceives to be invisible. Yet this strange 
paradox is not only universally received, but con- 
sidered as one of the noblest discoveries of mo- 
dern philosophy. The ingenious Addison, in 
the Spectator, No. 413, speaks thus of it: "I 
" have here supposed, that my reader is acquaint- 
" ed with that great modern discovery, which is 
" at present universally acknowledged by all the 
" inquirers into natural philosophy, namely, that 
rc light and colours, as apprehended by the ima- 
" gination, are only ideas in the mind, and not 
" qualities that have any existence in matter. 
" As this is a truth, which has been proved in- 
" contestibly by many modern philosophers, and 
" is indeed one of the finest speculations in 
" that science, if the English reader would see 
<c the notion explained at large, he may find it 
" in the eighth chapter of the second book of 
" Locke's Essay on Human Understanding J 



it 

■a' 



SECT. 5. OF SEEING* lOl 

Mr. Locke and Mr. Addison are writers who 
have deserved so well of mankind, that one must 
feel some uneasiness in differing from them, and 
would wish to ascribe all the merit that is due to 
a discovery upon which they put so high a value. 
And indeed it is just to acknowledge, that Locke, 
and other modern philosophers on the subject of 
secondary qualities, have the merit of distinguish- 
ing more accurately than those that went before 
them, between the sensation in the mind, and 
that constitution or quality of bodies which gives 
occasion to the sensation. They have shown 
clearly that these two things are not only dis- 
tinct, but altogether unlike: that there is no si- 
militude between the effluvia of an odorous body 
and the sensation of smell, or between the vibra- 
tions of a sounding body, and the sensation of 
sound: that there can be no resemblance between 
the feeling of heat, and the constitution of the 
heated body which occasions it: or between the 
appearance which a coloured body makes to the 
eye, and the texture of the body which causes 
that appearance. 

Nor was the merit small of distinguishing these 
things accurately; because, however different 
and unlike in their nature, they have been always 
so associated in the imagination, as to coalesce as 
it were into one two-faced form, which from its 
amphibious nature, could not justly be appropri- 
ated either to body or mind; and, until it was 
properly distinguished into its different constitu- 
ent parts, it was impossible to assign to either 

L 



162 OF THE HUMAN MIND. [CHAP. 6. 

their just shares in it. None of the ancient phi- 
losophers had made this distinction. The fol- 
lowers of Democritus and Epicurus conceived 
the forms of the heat, and sound, and colour, to 
be in the mind only, but that our senses fallaci- 
ously represented them as being in bodies. The 
Peripatetics imagined, that those forms are really 
in bodies ; and that the images of them are con- 
veyed to the mind by our senses. 

The one system made the senses naturally fal- 
lacious and deceitful; the other made the quali- 
ties of body to resemble the sensations of the 
mind. Now was it possible to find a third, with- 
out making the distinction we have mentioned; 
by which indeed the errors of both these ancient 
systems are avoided, and we are not left under 
the hard necessity of believing, either, on the 
one hand, that our senations are like to the qua- 
lities of body, or on the other, that God hath 
given us one faculty to deceive us, and another 
to detect the cheat. 

We desire, therefore, with pleasure, to do jus- 
tice to the doctrine of Locke, and other modern 
philosophers, with regard to colour, and other 
secondary qualities, and to ascribe to it its due 
merit, while we beg leave to censure the language 
in which they have expressed their doctrine. 
When they had explained and established the 
distinction between the appearance which colour 
makes to the eye, and the modification of the co- 
loured body, which, by the laws of Nature, causes 
that appearance ; the question was, whether to give 



SECT. 6.] OF SEEING. l6S 

the name of colour to the cause, or to the effect? 
by giving it, as they have done, to the effect, 
they set philosophy apparently in opposition to 
common sense, and expose it to the ridicule of 
the vulgar. But, had they given the name of co- 
lour to the cause, as they ought to have done, they 
must then have affirmed, with the vulgar, that co- 
lour is a quality of bodies; and that there is neither 
colour, nor any thing like it, in the mind. Their 
language, as well as their sentiments, would have 
been perfectly agreeable to the common appre- 
hensions of mankind, and true philosophy would 
have joined hands with Common Sense. As 
Locke was no enemy to common sense, it may be 
presumed, that, in this instance, as in some others, 
he was seduced by some received hypothesis: 
and, that this was actually the case, will appear 



in the following section. 



SECT. VL 



That none of our sensations are resemblances of any 
of the qualities of bodies. 

A± second inference is, That although colour is 
really a quality of body, yet it is not represented 
to the mind by an idea or sensation that resem- 
bles it; on the contrary, it is suggested by an 
idea which dees not in the least resemble it. — 
And this inference is applicable, not to colour 

L C Z 



164 OF THE HUMAN MIND. [CHAP. 6. 

only, but to all the qualities of body which we 
have examined. 

It deserves to be remarked, that in the analysis 
we have hitherto given of the operations of the 
five senses, and of the qualities of bodies disco- 
vered by them, no instance hath occurred, either 
of any sensation which resembles any quality of 
body, or of any quality of body whose image or 
resemblance is conveyed to the mind by means 
of the senses. 

There is no phenomenon in nature more unac- 
countable, than the intercourse that is carried on 
between the mind and the external world; there 
is no phenomenon which philosophical spirits 
have shown greater avidity to pry into and to 
resolve. It is agreed by all, that this intercourse 
is carried on by means of the senses: and this 
satisfies the vulgar curiosity, but not the philo- 
sophic. Philosophers must have some system, 
some hypothesis, that shews the manner in which 
our senses make us acquainted with external 
things. All the fertility of human invention 
seems to have produced only one hypothesis for 
this purpose, which therefore hath been univer- 
sally received; and that is, that the mind, like 
the mirror, receives the images of things from 
without, by means of the senses; so that their 
use must be to convey these images into the 
mind. 

Whether to these images of external things in 
the mind, we give the name of sensible forms or 
sensible species, with the Peripatetics, or the name 



SECT. 6.] OF SEEING. 165 

of ideas of sensation, with Locke; or whether, 
with later philosophers, we distinguish sensations, 
which are immediately conveyed by the senses, 
from ideas of sensation, which are faint copies of 
our sensations retained in the memory and ima- 
gination; these are only differences about words. 
The hypothesis I have mentioned is common to 
all these different systems. 

The necessary and allowed consequence of this 
hypothesis is, That no material thing, nor any 
quality of material things, can be conceived by 
us, or made an object of thought, until its image 
is conveyed to the mind by means of the senses. 
We shall examine this hypothesis particularly 
afterwards, and at this time only observe, that, in 
consequence of it, one would naturally expect, 
that to every quality or attribute of body w T e 
know or can conceive there should be a sensa- 
tion corresponding, which is the image and re- 
semblance of that quality; and that the sensa- 
tions which have no similitude or resemblance to 
body, or to any of its qualities, should give us no 
conception of a material world, or of any thing 
belonging to it. These things might be expect- 
ed as the natural consequence of the hypothesis 
we have mentioned. 

Now, we have considered, in this and the pre- 
ceding chapters, extension, figure, solidity, mo- 
tion, hardness, roughness, as well as colour, heal 
and cold, sound, taste, and smell. We have en- 
deavoured to shew, that our nature and constitu- 
tion lead us to conceive these as qualities of body, 

l 3 



I6t> OF THE HUMAN MIND. [CHAP. 6. 

as all mankind have always conceived them to be. 
We have likewise examined with great attention, 
the various sensations we have by means of the 
five senses, and are not able to find among them 
all, one single image of body, or of any of its 
qualities. "From whence then come those images 
of body and of its qualities into the mind? Let 
philosophers resolve this question. All I can say 
is, that they come not by the senses. I am sure, 
that, by proper attention and care, I may know 
my sensations, and be able to affirm with certain- 
ty what they resemble, and what they do not re- 
semble. I have examined them one by one, and 
compared them with matter and its qualities; 
and I cannot find one of them that confesses a 
resembling feature. 

A truth so evident as this, That our sensations 
are not images of matter, or of any of its quali- 
fies, ought not to yield to a hypothesis such as 
that above mentioned, however ancient, or how- 
ever universally received by philosophers; nor 
can there be any amicable union between the two. 
This will appear by some reflections upon the 
spirit of the ancient and modern philosophy con- 
cerning sensation. 

During the reign of the Peripatetic philoso- 
phy, our sensations were not mutually or accu- 
rately examined. The attention of philosophers, 
as well as of the vulgar, was turned to the things 
signified by them: therefore, in consequence of 
the common hypothesis, it was taken for granted, 
that all the sensations we have from external 



SECT. 6.] OF SEEING* 167 

things, are the forms or images of these external 
things. And thus the truth we have mentioned, 
yielded entirely to the hypothesis, and was alto- 
gether suppressed by it. 

Des Cartes gave a noble example of turning 
Our attention inward, and scrutinizing our sensa- 
tions; and this example hath been very worthily 
followed by modern philosophers, particularly by 
Malebranche, Locke, Berkeley, and Hume. 
The effect of this scrutiny hath been a gradual 
discovery of the truth above mentioned, to wit, 
the dissimilitude between the sensations of our 
minds, and the qualities or attributes of an in- 
sentient inert substance, such as we conceive 
matter to be. But this valuable and useful dis- 
covery, in its different stages, hath still been un- 
happily united to the ancient hypothesis; and, 
from this inauspicious match of opinions, so un- 
friendly and discordant in their natures, have 
arisen those monsters of paradox and scepticism 
with which the modern philosophy is too justly 
chargeable. 

Locke saw clearly, and proved incontestably, 
that the sensations we have by taste, smell, and 
hearing, as well as the sensations of colour, heat, 
and cold, are not resemblances of any thing in bo- 
dies; and in this he agrees with Des Cartes and 
Malebranche. Joining this opinion with the 
hypothesis, it follows necessarily, that three 
senses of the five are cut off from giving us anv 
intelligence of the material world, as being alto- 
gether inept for that office. Smell, and taste,: 



168 OF THE HUMAN MIND. [CHAP. 6. 

and sound, as well as colour and heat, can have 
no more relation to body, than anger or gratitude ; 
nor ought the former to be called qualities of 
body, whether primary or secondary, any more 
than the latter. For it was natural and obvious 
to argue thus from that hypothesis; If heat, and 
colour and sound, are real qualities of body, the 
sensations, by which we perceive them, must be 
resemblances of those qualities; but these sensa- 
tions are not resemblances; therefore those are 
not real qualities of body. 

AVe see then, that Locke, having found that 
the ideas of secondary qualities are no resem- 
blances, was compelled, by a hypothesis common 
to all philosophers, to deny that they are real 
qualities of body. It is more difficult to assign a 
reason, why, after this he should call them secon* 
dary qualities; for this name, if I mistake not, 
was of his invention. Surely he did not mean 
that they wore secondary qualities of the mind; 
and I do not see with what propriety, or even by 
what tolerable licence, he could call them secon- 
dary qualities cf body, after finding that they 
were no qualities of body at all. In this he seems 
to have sacrificed to Common Sense, and to have 
been led by her authority, even in opposition to 
his hypothesis. The same sovereign mistress of 
our opinions that led this philosopher to call those 
things secondary qualities of body, which accord- 
ing to his principles and reasonings, were ' no 
qualities of body at all, hath led, not the vulgar 
of-all ages only, but philosophers also, and even 



SECT. 6.] OF SEEING. l69 

the disciples of Locke, to believe them to be real 
qualities of body: she hath led them to investi- 
gate, by experiments, the nature of colour, and 
sound, and heat, in bodies: Nor hath this ives- 
tigation been fruitless, as it must have been, if 
there had been no such thing in bodies; on the 
contrary it hath produced very noble and useful 
discoveries, which make a very considerable part 
of natural philosophy. If then natural philoso- 
phy be not a dream, there is something in bo- 
dies which we call colour, and heat and sound. 
And if this be so, the hypothesis from which the 
contrary is concluded, must be false: for the ar- 
gument, leading to a false conclusion, recoils 
against the hypothesis from which it was drawn, 
and thus directs its force backward. If the qua- 
lities of body were known to us only by sensations 
that resemble them, then colour, and sound, and 
heat, could be no qualities of body; but these are 
real qualities of body ; and therefore the qualities 
of body are not known only by means of sensa- 
tions that resemble them. 

But to proceed: What Locke hath proved with 
regard to the sensations we have by smell, taste, 
and hearing, Bishop Berkeley proved no less 
unanswerably with regard to all our other sen- 
sations; to wit, that none of them can in the 
least resemble the qualities of a lifeless and in- 
sentient being, such as matter is conceived to be. 
Mr. Hume hath confirmed this by his authori- 
ty and reasoning. This opinion surely looks with 
a very malign aspect upon the old hypothesis; 



1/0 OF THE HUMAN MIND. [CHAP. 6. 

yet that hypothesis hath still been retained, and 
conjoined with it. And what a brood of mon- 
sters hath this produced! 

The first born of this union, and perhaps the 
most harmless was, That the secondary qualities 
of body were mere sensations of the mind. To 
pass by Malebranche's notion of seeing all things 
hi the ideas of the divine mind, as a foreigner 
never naturalized in this island; the next was 
Berkeley's system, That extension, and figure, 
and hardness, and motion; that land, and sea, 
and houses, and our own bodies, as well as those 
of our wives, and children, and friends, are no- 
thing but ideas of the mind; and that there is 
nothing existing in nature, but minds and ideas. 
The progeny that followed, is still more fright- 
ful ; so that it is surprising, that one could be 
found who had the courage to act the midwife 
to rear it up, and to usher it into the world. No 
causes nor effects; no substance, material or 
spiritual; no evidence even in mathematical de- 
monstration: no liberty nor active power; no- 
thing existing in nature, but impressions and ideas 
following each other, without time, place or sub- 
ject. Surely no age ever produced such a sys- 
stem of opinions, justly deduced with great acute- 
ness, perspicuity, and elegance, from a principle 
universally received. The hypothesis we have 
mentioned, is the father of them all. The dis- 
similitude of our sensations and feeliegs to exter- 
nal things, is the innocent mother of most of 
them 



SECT. 6.] OF SEEING. 171 

As it happens sometimes in an arithmetical 
operation, that two errors balance one another, so 
that the conclusion is little or nothing affected 
by them; but when one of them is corrected, 
and the other left, we are led farther from the 
truth, than by both together: so it seems to have 
happened in the Peripatetic philosophy of sensa- 
tion, compared with the modern. The Peripa- 
tetics adopted two errors; but the last served as 
a corrective to the first, and rendered it mild and 
gentle; so that their system had no tendency to 
scepticism. The moderns have retained the first 
of those errors, but have gradually detected and 
corrected the last. The consequence hath been, 
that the light we have struck out hath created 
darkness, and scepticism hath advanced hand in 
hand with knowledge, spreading its melancholy 
gloom, first over the material world, and at last 
over the whole face of nature. Such a pheno- 
menon as this, is apt to stagger even the lovers 
of light and knowledge, while its cause is latent ; 
but when that is detected, it may give hopes, that 
this darkness shall not be everlasting, but that it 
shall be succeeded by a more permanent light. 



172 OF THE HUMAN MIND. [CHAP. 6. 



SECT. VII. 

Of risible figure and extension. 

Although there is no resemblance, nor as far 
as we know any necessary connection between 
that quality in a body which we call its colour, 
and the appearance which that colour makes to 
the eye; it is quite otherwise with regard to its 
figure and magnitude. There is certainly a re- 
semblance, and a necessary connection, between 
the visible figure and magnitude of a body, and 
its real figure and magnitude; no man can give a 
reason why a scarlet colour affects the eye in the 
manner it does; no man can be sure that it affects 
his eye in the same manner as it affects the eye 
of another, and that it has the same appearance 
to him as it has to another man; but we can 
assign a reason why a circle placed obliquely to 
the eye, should appear in the form of an ellipse. 
The visible figure, magnitude, and position, may, 
by mathematical reasoning, be deduced, from the 
real: and it may be demonstrated, that every eye 
that sees distinctly and perfectly, must in the 
same situation, see it under this form, and no 
other. Nay, we may venture to affirm, that a man 
born blind, if he were instructed in mathematics, 
would be able to determine the visible figure of a 
body, when its real figure, distance, and position, 
are given- Dr. Saunderson understood the pro- 



SECT. 7.] OF SEEING. 173 

jection of the sphere, and perspective. Now, I 
require no more knowledge in a blind man, in 
order to his being able to determine the visible 
figure of bodies, than that he can project the out- 
line of a given body, upon the surface of a hollow 
sphere, whose centre is in the eye. This pro- 
jection is the visible figure he wants; for it is the 
same figure with that which is projected upon 
the tunica retina in vision. 

A blind man can conceive lines drawn from 
every point of the object to the centre of the eye, 
making angles. He can conceive that the length 
of the object will appear greater or less, in pro- 
portion to the angle which it subtends at the eye; 
and that in like manner, the breadth, and in gene- 
ral the distance of any one point of the object from 
any other point, will appear greater or less, in pro- 
portion to the angles which those distances sub- 
tend. He can easily be made to conceive, that 
the visible appearance has no thickness, any more 
than a projection of the sphere, or a perspective 
draught. He may be informed that the eye, un- 
til it is aided by experience, does not represent 
one object as nearer or more remote than another, 
Indeed he would probably conjecture this of him- 
self, and be made apt to think that the rays of 
light must make the same impression upon the 
eye, whether they come from a greater or a less 
distance. 

These are all the principles which we suppose 
our blind mathematician to have; and these he 
may certainly acquire by information and reflec- 



17^ OF THE HUMAN MIND. [CHAP. 6. 

tion. It is no less certain, that from these prin- 
ciples, having given the real figure and magni- 
tude of a body, and its position and distance with 
regard to the eye, he can find out its visible fi- 
gure and magnitude. He can demonstrate in 
general, from these principles, that the visible fi- 
gure of all bodies will be the same with that of 
their projection upon the surface of a hollow 
sphere, when the eye is placed in the centre. 
And he can demonstrate, that their visible mag- 
nitude will be greater or less, according as their 
projection occupies a greater or less part of the 
surface of this sphere. 

To set this matter in another light, let us dis- 
tinguish betwixt the positio?i of objects with re- 
gard to the eye, and their distance from it. Ob- 
jects that lie in the same right line drawn from 
the centre of the eye, have the same position, 
however different their distances from the eye 
may be: but objects which lie in different right 
lines drawn from the eye's centre, have a differ- 
ent position; and this difference of position is 
greater or less, in proportion to the angle 
made at the eye by the right lines mentioned. 
Having thus defined what we mean by the posi- 
tion of objects with regard to the eye, it is evi- 
dent, that as the real figure of a body consists in 
the situation of its several parts with regard to 
one another, so its visible figure consists in the 
position of its several parts with regard to the 
eye; and as he that hath a distinct conception 
of the situation of the parts of the body with re- 



SECT. 7-] OP SEEING* 1J5 

gard to one another, must have a distinct concep- 
tion of its real figure; so that he conceives dis- 
tinctly the position of its several parts with regard 
to the eye, must have a distinct conception of 
its visible figure. Now, there is nothing surely 
to hinder a blind man from conceiving the posi- 
tion of the several parts of a body with regard to 
the eye, any more than from conceiving their 
situation with regard to one another; and there- 
fore, I conclude, that a blind man may attain a 
distinct conception of the visible figure of bodies. 

Although we think the arguments that have 
been offered are sufficient to prove, that a blind 
man may conceive the visible extension and fi- 
gure of bodies; yet, in order to remove some 
prejudices against this truth, it will be of use to 
compare the notion which a blind mathematician 
might form to himself of visible figure, with that 
which is presented to the eye in vision, and to 
observe wherein they differ. 

First, Visible figure is never presented to the 
eye but in conjunction with colour; and although 
there be no connection between them from the 
nature of the things, yet, having, so invariably 
kept company together, we are hardly able to 
disjoin them even in our imagination. What 
mightily increases this difficulty is, that we have 
never been accustomed to make visible figure an 
object of thought. It is only used as a sign, and, 
having served this purpose, passes away, without 
leaving a trace behind. The drawer or designer, 
whose business it is to hunt this fugitive form. 



176 OF THE HUMAN MIND. [CHAP. 6. 

and to take a copy of it, finds how difficult his 
task is, after many years labour and practice. 
Happy! if at last he can acquire the art of ar- 
resting it in his imagination, until lie can delineate 
it. For then it is evident, that he must be able 
to draw as accurately from the life as from a 
copy. But how few of the professed masters of 
designing are ever able to arrive at this degree 
of perfection? it is no wonder, then, that we 
should find so great difficulty in conceiving this 
form apart from its constant associate, when it is 
so difficult to conceive it at all. But our blind 
man's notion of visible figure will not be associat- 
ed with colour, of which he hath no conception ; 
but it will perhaps be associated with hardness or 
smoothness, with which he is acquainted by 
touch. These different associations are apt to 
impose upon us, and to make things seem differ- 
ent, which in reality are the same. 

Secondly, The blind man forms the notion of 
visible figure to himself, by thought, and by ma- 
thematical reasoning from principles; whereas 
the man that sees, has it presented to his eye 
at once, without any labour, without any reason- 
ing by a kind of inspiration. A man may form 
to himself the notion of a parabola or a cycloid, 
from the mathematical definitions of those figures, 
although he had never seen them drawn or de- 
lineated. Another, who knows nothing of the ma- 
thematical definitions of the figures, may see them 
delineated on paper, or feel them cut out on wood. 
Each may have a distinct conception of the fi- 



SECT. 8.] OF SEEING. 1?7 

gures, one by mathematical reasoning, the other 
by sense. Now, the blind man forms his notion 
of visible figure in the same manner as the first 
of these formed his notion of a parabola or a cy- 
cloid, which he never saw. 

Third, Visible figure leads the man that sees, 
directly to the conception of the real figure, of 
which it is a sign, But the blind man's thoughts 
move in a contrary direction. For he must first 
know the real figure, distance, and situation, of 
the body, and from thence he slowly traces out 
the visible figure by mathematical reasoning. 
Nor does his nature lead him to conceive this 
visible figure as a sign ; it is a creature of his own 
reason and imagination. 



SECT. VIII. 



Some queries concerning visible figure anewered. 

It may be asked, What kind of thing is this visi- 
ble figure? Is it a sensation or an idea? If it 
is an idea, from what sensation is it copied? 
These questions may seem trivial or impertinent 
to one who does not know, that there is a tribu- 
nal of inquisition erected by certain modern 
philosophers before which every thing in nature 
must answer. The articles of inquisition are few 
indeed, but very dreadful in their consequence-. 
They are only these: Is the prisoner an impres- 



M 



1?8 OF THE HUMAN MIND. [CHAP. 6. 

sion or an idea? If an idea, from what impres- 
sion copied? Now, if it appears that the pri- 
soner is neither an impression or an idea copied 
from some impression, immediately, without be- 
ing allowed to offer any thing in arrest of judg- 
ment, he is sentenced to pass out of existence, 
and to be, in all time to come, an empty un- 
meaning sound, or the ghost of a departed en- 
tity. 

Before this dreadful tribunal, cause and effect, 
time and place, matter and spirit, have been tri- 
ed and cast: how then shall such a poor flimsy 
form as visible figure stand before it? It must 
even plead guilty, and confess that it is neither 
an impression nor an idea. For alas! It is no- 
torious, that it is extended in length and breadth ; 
it may be long or short, broad or narrow, tri- 
angular, quadrangular, or circular: and there- 
fore, unless ideas and impressions are extend- 
ed and figured, it cannot belong to that cate- 
gory- 

If it should still be asked, To what category of 
beings does visible figure then belong? I can 
only, in answer, give some token, by which those 
who are better acquainted with the categories 
may chance to find its place. It is, as we have 
said, the position of the several parts of a figured 
body, with regard to the eye. The different po- 
sitions of the several parts of the body with re- 
gard to the eye, when put together, make a real 
figure, which is truly extended in length and 
breadth, and which represents a figure that is ex- 



SECT. 8.] OF SEEING. 179 

tended in length, breadth, and thickness. In like 
manner the projection of the sphere is a real 
figure, and hath length and breadth, but repre- 
sents the sphere which hath three dimensions. A 
projection of the sphere, or a perspective view of 
a palace, is a representative in the very same 
sense as visible figure is, and wherever they have 
their lodgings in the categories, this will be found 
to dwell next door to them. 

It may farther be asked, Whether there be any 
sensation proper to visible figure, by which it is 
suggested in vision? Or by what means it is pre- 
sented to the mind? This is a question of some 
importance, in order to our having a distinct no- 
tion of the faculty of seeing: and to give all the 
light to it we can, it is necessary to compare this 
sense with other senses, and to make some sup- 
positions, by which we may be enabled to distin- 
guish things that are apt to be confounded, al- 
though they are totally different. 

There are three of our senses which give us 
intelligence of things at a distance: smell, hearing 
and sight. In smelling, and in hearing, we have 
a sensation or impression upon the mind, which, 
by our constitution, we conceive to be a sign of 
something external: but the position of this ex- 
ternal thing, with regard to the organ of sense, 
is not presented to the mind along with the sen- 
sation. When 1 hear the sound of a coach, I 
could not previous to experience, determine 
whether the sounding body was above or below, 
to the right hand or to the left. So that the sen- 

m 2 



180 OF THE HUMAN MIND. [CHAP. 6. 

sation suggests to me some external object as the 
cause or occasion of it; but it suggests not the 
position of that object, whether it lies in this di- 
rection or in that. The same thing may be said 
with regard to smelling. But the case is quite 
different with regard to seeing. When I see an 
object, the appearance which the colour of" it 
makes, may be called the sensation, which sug- 
gests to me some external thing as its cause; but 
it suggests likewise the individual direction and 
position of this cause with regard to the eye. I 
know it is precisely in such a direction, and in 
no other. At the same time, I am not conscious 
of any thing that can be called sensation, but the 
sensation of colour. The position of the colour- 
ed thing is no sensation, but it is by the laws of 
my constitution presented to the mind along with 
the colour, without any additional sensation. 

Let us suppose, that the eye were so constitut- 
ed, that the rays coming from any one point of 
the object were not, as they are in our eyes, col- 
lected in one point of the retina, but diffused over 
the whole: It is evident to those who understand 
the structure of the eye, that such an eye as we 
have supposed, would show the colour of a body 
as our eyes do, but that it would neither shew 
figure nor position. The operation of such an- 
eve would be precisely similar to that of hearing 
and smell; it would give no perception of figure 
or extension, but merely of colour. Nor is the 
supposition we have made altogether imaginary: 
for it is nearly the case of most people who have 



SECT. 8.] OF SEEING. 181 

cataracts, whose crystalline, as Mr. Ciieselden 
observes, does not altogether exclude the rays of 
light, but diffuses them over the retina, so that 
such persons see things as one does through a 
glass of broken jelly : they perceive the colour, 
but nothing of the figure or magnitude of objects. 

Again, if we should suppose, that smell and 
sound were conveyed in right lines from the ob- 
jects, and that every sensation of hearing and 
smell suggested the precise direction or position 
of its object; in this case, the operations of hear- 
ing and smelling would be similar to that of see- 
ins;; we should smell and hear the figure of ob- 
jects, in the same sense as now we see it; and 
every smell and sound would be associated with 
some figure in the imagination, as colour is in our 
present state. 

We have reason to believe, that the rays of 
light make some impression upon the retina; but 
we are not conscious of this impression; nor have 
anatomists or philosophers been able to discover 
the nature and effects of it; whether it produces a 
vibration in the nerve, or the motion of some sub- 
tile fluid contained in the nerve, or something 
different from either, to which we cannot give a 
name. -Whatever it is, we shall call it the mate? nil 
impression ; remembering carefully, that it is not 
an impression upon the mind, but upon the body; 
and that it is no sensation, or can resemble sensa- 
tion any more than figure or motion can resemble 
thought. Xow, this material impression, made 
upon a particular point of the retina, by the laws of 

M 3 



182 OF THE HUMAN MIND. [CHAP. 6. 

our constitution, suggests two tilings to the mind, 
namely, the colour, and the position of some ex- 
ternal object. No man can give a reason, why 
the same material impression might not have sug- 
gested sound, or smell, or either of these, along 
with the position of the object. That it should 
suggest colour and position, and nothing else, we 
can resolve only into our constitution, or the will 
of our Maker. And since there is no necessary 
connection between these two things suggested 
by this material impression, it might, if it had so 
pleased our Creator, have suggested one of them 
without the other. Let us suppose, therefore, 
since it plainly appears to be possible that our 
eyes had been so framed as to suggest to us the 
position of the object, without suggesting colour 
or any other quality: What is the consequence 
of this supposition? It is evidently this, that the 
person endued with such an eye, would perceive 
the visible figure of bodies, without having any 
sensation or impression made upon his mind. 
The figure he perceives is altogether external, 
and therefore cannot be called an impression upon 
the mind, without the grossest abuse of language. 
If it should be said, that it is impossible to per- 
ceive a figure, unless there be some impression of 
it upon the mind; I beg leave not to admit the 
impossibility of this, without some proof: and I 
can find none. Neither can I conceive what is 
meant by an impression of figure upon the mind. 
I can conceive an impression of figure upon wax, 
or upon any body that is lit to receive it; but an 



SECT. 8.] OF SEEING. 183 

impression of it upon the mind, is to me quite 
unintelligible; and although I form the most dis- 
tinct conception of figure, I cannot, upon the 
strictest examination, find any impression of it 
upon my mind. 

If we suppose, last of all, that the eye hath 
the power restored of perceiving colour, I appre- 
hend that it will be allowed, that now it perceives 
figure in the very same manner as before, with 
this difference only, that colour is always joined 
with it. 

In answer, therefore, to the question proposed, 
there seems to be no sensation that is appropriat- 
ed to vision figure, or whose oiiice it is to sug- 
gest it. It seems to be suggested immediately 
by the material impression upon the organ of 
which we are not conscious: and why may not a 
material impression upon the retina suggest visi- 
ble figure, as well as the material impression made 
upon the hand, when we grasp a ball, suggests 
real figure? In the one case one and the same 
material impression, suggests both colour and 
visible figure; and in the other case, one and 
the same material impression suggests hardness, 
heat, or cold, and real figure, all at the same 
time. 

We shall conclude this section with another 
question upon this subject. Since the \ isible fi- 
gure of bodies is a real and external object to 
the eye, as their tangible figure is to the touch: 
it may be asked, whence arises the diHjculty of 
attending to the first, and the facility of attending 



L8i OF T.HE HUMAN MIND. [CHAP. 6. 

to the last? It is certain, that the first is more 
frequently presented to the eye, than the last is 
to the touch; the first is as distinct and deter- 
minate an object as the last, and seems in its 
own nature as proper for speculation. Yet so 
little hath it been attended to, that it never had 
a name in any language, until Bishop Berkeley 
gave it that which we have used after his example, 
to distinguish it from the figure which is the ob- 
ject of touch. 

The difficulty of attending to the visible figure 
of bodies, and making it an object of thought,, 
appears so similar to that which we find in at- 
tending to our sensations, that both have proba- 
bly like causes. Nature intended the visible 
figure as a sign of the tangible figure and situa- 
tion of bodies, and hath taught us by a kind of 
instinct to put it always to this use. Hence it 
happens, that the mind passes over it with a ra- 
pid motion, to attend to the things signified by 
it. It is as unnatural to the mind to stop at the 
visible figure, and attend to it, as it is to a spheri- 
cal body to stop upon an inclined plane. There 
is an inward principle, which constantly carries 
it forward, and which cannot be overcome but 
by a contrary force. 

There are other external things which nature 
intended for signs; and we find this common to 
them all, that the mind is disposed to overlook 
them, and to attend only to the tilings signified 
bv them. Thus, there are certain modifications 
of the human face, which are natural si<rns of the 



SECT. 8.] OF SEEING. 18.5 

present disposition of the mind. Every man nn* 
derstands the meaning of these signs, but not 
one of a hundred ever attended to the signs 
themselves, or knows any thing about them. 
Hence you may find many an excellent practical 
physiognomist, who knows nothing of the pro- 
portions of a face, nor can delineate or describe 
the expression of any one passion. 

An excellent painter or statuary can tell, not 
only what are the proportions of a good face, but 
what changes every passion makes in it. This, 
however, is one of the chief mysteries of his art, 
to the acquisition of which, infinite labour and 
attention, as well as a happy genius, are required. 
But when he puts his art in practice, and happi- 
ly expresses a passion by its proper signs, every 
one understands the meaning of these signs> with- 
out art, and without reflection. 

What has been said of painting, might easily 
be applied to all the fine arts. The difficulty hi 
them all consists in knowing and attending to 
those natural signs, whereof every man under- 
stands the meaning. 

We pass from the sign to the thing signified, 
with ease, and by natural impulse; but to go 
backward from the thing signified to the sign, is 
a work of labour and difficulty. Visible figure, 
therefore, being intended by nature to be a sign, 
we pass on immediately to the thing signified, 
and cannot easily return to give any attention to 
the sign. 

Nothing shews more clearly our indisposition 



186 OF THE HUMAN MIND. [CHAP. 6, 

to attend to visible figure and visible extension 
than this, that although mathematical reasoning 
is no less applicable to them, than to tangible fi- 
gure and extension, yet they have entirely escap- 
ed the notice of mathematicians. While that fi- 
gure and that extension, which are objects of 
touch, have been tortured ten thousand ways for 
twenty centuries, and a very noble system of 
science has been drawn out of them; not a sin- 
gle proposition do we find with regard to the fi- 
gure and extension which are the immediate ob- 
jects of sight? 

When the geometrician draws a diagram with 
the most perfect accuracy; w T hen he keeps his 
eye fixed upon it, while he goes through a long 
process of reasoning, and demonstrates the rela- 
tions of the several parts of his figure; he does 
not consider, that the visible figure presented to 
his eye, is only the representative of a tangible 
figure, upon which all his attention is fixed; he 
does not consider that these two figures have 
really different properties; and that what he de- 
monstrates to be true of the one, is not true of 
the other. 

This perhaps will seem so great a paradox, 
even to mathematicians, as to require demonstra- 
tion before it can be believed, Nor is the de- 
monstration at all difficult, if the reader will have 
patience to enter but a little into the mathemati- 
cal consideration of visible figure, which we shall 
call the geometry of visibks. 



SECT. 9/J OF SEEING. 187 

SECT. IX. 

Of the geometry of visibles. 

In this geometry, the definitions of a point of a 
line, whether straight or curve; of an angle 
whether acute, or right, or obtuse; and of a cir- 
cle, are the same as in common geometry. The 
mathematical reader will easily enter into the 
whole mystery of this geometry, if he attends 
duly to these few evident principles. 

1. Supposing the eye placed in the centre of a 
sphere, every great circle of the sphere will 
have the same appearance to the eye as if it was 
a straight line. For the curviture of the circle 
being turned directly toward the eye, is not per- 
ceived by it. And for the same reason, any line 
which is drawn in the plane of a great circle of 
the sphere, whether it be in reality straight or 
curve, will appear straight to the eye. 

2. Every visible right line will appear to coin- 
cide with some great circle of the sphere; and 
the circumference of that great circle, even when 
it is produced until it returns into itself will ap- 
pear to be a continuation of the same visible right 
line, all the parts of it being visibly in directum. 
For the eye, perceiving only the position of ob- 
jects with regard to itself, and not their distance, 
will see those points in the same visible place 
which have the same position with regard to the 



188 OF THE HUMAN MIND. [CHAP. 0. 

eye, bow different soever their distances from 
it may be. Now since a plane passing through 
the eye and a given visible right line, will be 
the plane of some great circle of the sphere, 
every point of the visible right line will have the 
same position as some point of the great circle; 
therefore they will both have the same visible 
place, and coincide to the eye: and the whole 
circumference of the great circle continued even 
until it returns into itself, will appear to be a 
continuation of the same visible right line. 
Hence it follows : 

3. That every visible right line, when it is con- 
tinued in directum, as far as it may be continued, 
will be represented by a great circle of a sphere, 
in whose centre the eye is placed. It follows, 

4. That the visible angle comprehended under 
two visible right lines, is equal to the spherical 
angle comprehended under the two great circles 
which are the representatives of these visible 
lines. For since the visible lines appear to co- 
incide with the great circles, the visible angle 
comprehended under the former, must be equal 
to the visible angle comprehended under the lat- 
ter. But the visible angle comprehended under 
the two great circles, when seen from the centre, 
is of the same magnitude with the spherical angle 
which they really comprehend, as mathematicians 
know; therefore the visible angle made by any 
two visible lines, is equal to the spherical angle 
made by the two great circles of the sphere which 
are their representatives. 



SECT. 9.] OF SEEING. 189 

5. Hence it is evident, that every visible right* 
lined triangle, will coincide in all its parts with 
some spherical triangle. The sides of the one 
will appear equal to the sides of the other, and 
the angles of the one to the angles of the other, 
each to each; and therefore the whole of the 
one triangle will appear equal to the whole of the 
other. In a word, to the eye they will be one 
and the same, and have the same mathematical 
properties. The properties therefore of visible 
right lined triangles, are not the same w r ith the 
properties of plain triangles, but are the same 
with those of spherical triangles. 

6. Every lesser circle of the sphere, will appear 
a circle to the eye, placed as we have supposed 
all along, in the centre of the sphere. And, on 
the other hand, every visible circle will appear to 
coincide with some lesser circle of the sphere. 

7. Moreover, the whole surface of the sphere 
will represent the whole of visible space: for 
since every visible point coincides with some 
point of the surface of the sphere, and has the 
same visible place, it follows, that all the parts of 
the spherical surface taken together, will repre- 
sent all possible visible places, that is, the whole 
of visible space. And from this it follows, in the 
last place, 

8. That every visible figure will be represented 
by that part of the surface of the sphere, on which 
it might be projected, the eye being in the centre. 
And every such visible figure will bear the same 
ratio to the whole of visible space, as the part of 



19Q OF THE HUMAN MIND. [CHAP. 6. 

the spherical surface which represents it bears to 
the whole spherical surface. 

The mathematical reader, I hope, will enter 
into these principles with perfect facility, and 
will as easily perceive, that the following propo- 
sitions with regard to visible figure and space, 
which we offer only as a specimen, may be ma- 
thematically demonstrated from them, and are 
not less true nor less evident than the propositions 
(if Euclid, with regard to tangible figures. 

Prop. 1. Every right line being produced, will 
at last return into itself. 

2. A right line returning into itself, is the 
longest possible right line; and all other right 
lines bear a finite ratio to it. 

3. A right line returning into itself, divides the 
whole of visible space into two equal parts, 
which will both be comprehended under this 
right line. 

4. The whole of visible space bears a finite 
ratio to any part of it. 

5. Any two right lines being produced, will 
meet in two points, and mutually bisect each 
other. 

6. If two lines be parallel, that is, every where 
equally distant A om each other, they cannot both 
be straight. 

7'. Any right line being given, a point may be 
found, which is at the same distance from all the 
points of the given right line. 

8. A circle may be parallel to a right line, that 
is, may be equally distant from it in all its parts. 



SECT. 9-] OF SEEING. 191 

9. Right-lined triangles that are similar, are 
right angles. 

10. Of every right-lined triangle, the three 
angles taken together, are greater than two right 
angles. 

11. The angles of a right-lined triangle, may 
all be right angles, or all obtuse angles. 

12. Unequal circles are not as the squares of 
their diameters, nor are their circumferences in 
the ratio of their diameters. 

This small specimen of the geometry of visi- 
bles, is intended to lead the reader to a clear and 
distinct conception of the figure and extension 
which is presented to the mind by vision; and to 
demonstrate the truth of what we have affirmed 
above, namely, That those figures and that ex- 
tension which are the immediate objects of sight, 
are not the figures and the extension about which 
common geometry is employed; that the geome- 
trician, while he looks at his diagram, and demon- 
strates a proposition, hath a figure presented to his 
eye, which is only a sign and representative of a 
tangible figure; that he gives not the least atten- 
tion to the first, but attends only to the last; and 
that these two figures have different properties, 
so that what he demonstrates of the one, is not 
true of the other. 

It deserves, however, to to be remarked, that as 
a small part of a spherical surface differs not sen- 
sibly from a plane surface; so a small part of vi- 
sible extension differs very little from that exten- 
sion in length and breadth, which is the object 



192 OF THE HUMAN MIND. [CHAP. G. 

of touch. And it is likewise to be observed, that 
the human eye is so formed, that an object which 
is seen distinctly and at one view, can occupy 
but a small part of visible space; for we never 
see distinctly what is at a considerable distance 
from the axis of the eve; and therefore, when 
we would see a mrge object at one veiw, the eye 
must be at so great a distance, that the object 
occupies but a small part of visible space. From 
these two observations, it follows, that plain figures 
which, are seen at one veiw, when their planes are 
not oblique, but direct to the eye, differ little 
from the visible figures which they present to 
the eye. The several lines in the tangible figure 
have very nearly the same proportion to each 
other as in the visible; and the angles of the 
one are very nearly, although not strictly and 
mathematically, equal to those of the other. Al- 
though therefore we have found many instances 
of natural signs which have no similitude to the 
things signified, this is not the case with regard 
to visible figure. It hath in all cases such a si- 
militude to the thing signified by it, as a plan or 
profile hath to that which it represents; and in 
some cases the sign and thing signified have to 
all sense the same figure and the same propor- 
tions. If we could find a being endued with 
sight only, without any other external sense, and 
capable of reflecting and reasoning upon what 
he sees, the notions and philosophical specula- 
tions of such a being, might assist us in the diffi- 
cult task of distinguishing the perceptions which 



SECT. 9.] OF SEEINC- 193 

we have purely by sight, from those which de- 
rive their origin from other senses. Let us sup- 
pose such a being, and conceive as well as we 
can, what notion he would have of visible objects, 
and what conclusions he would deduce from them. 
We must not conceive him disposed by his con- 
stitution, as we are, to consider the visible ap- 
pearance as a sign of something else; it is no 
sign to him, because there is nothing signified by 
it; and therefore we must suppose him as much 
disposed to attend to the visible figure and ex- 
tension of bodies, as we are disposed to attend to 
their tangible figure and extension. 

If various figures are presented to his sense, 
he might, without doubt, as they grow familiar, 
compare them together, and perceive wherein 
they agree, and wherein they differ. He might 
perceive visible objects to havelengthandbreadth, 
but could have no notion of a third dimension, 
any more than we can have of a fourth. All vi- 
sible objects would appear to be terminated by 
lines, straight or curve ; and objects terminated 
by the same visible lines, would occupy the same 
place, and fill the same part of visible space. It 
would not be possible for him to conceive one 
object to be behind another, one to be near- 
er, another more distant. 

To us who conceive three dimensions, a line 
may be conceived straight; or it may be conceiv- 
ed incurvated in one dimension; and straight in 
another; or, lastly, it may be incurvated in two 
dimensions. Suppose a line to be drawn upwards 



194- OF th£ human mind. [chap. 6. 

unci downwards, its length makes one dimension 
which we shall call upwards and downwards ; and 
there are two dimensions remaining, according 
to which it may be straight or curve. It maybe 
bent to the right or to the left; and if it has no 
bending either to the right or left, it is straight 
in this dimension. But supposing it straight in 
this dimension of right and left, there is still ano- 
ther dimension remaining, in which it may be 
curve; for it maybe bent backwards or forwards. 
When we conceive a tangible straight line, we 
exclude curvature in either of these two dimen- 
sions: and as what is conceived to be excluded, 
must be conceived, as well as what is conceived 
to be included, it follows, that all the three di- 
mensions enter into our conception of a straight 
line. Its length is one dimension, its straightness 
in two other dimensions is included, or curvature 
in these two dimensions excluded, in the concep- 
tion of it. 

The being we have supposed, having no con- 
ception of more than two dimensions, of which 
the length of a line is one, cannot possibly con- 
ceive it either straight or curve in more than one 
dimension: so that in his conception of a right 
line, curvature to the right hand or left is ex- 
cluded; but curvature backwards or forwards 
cannot be excluded because he neither hath, nor 
can have, any conception of such curvature. 
Hence we see the reason that a line, which is 
straight to the eye, may return into itself: for its 
being straight to the eye, implies only straight- 



SECT. 9.] OF SEEING. 195 

ness in one dimension; and a line, which is 
straight in one dimension, may notwithstanding 
be curve in another dimension, and so may return 
into itself. 

To us who conceive three dimensions, a sur- 
face is that which hath length and breadth, ex- 
cluding thickness: and a surface may be either 
plain in this third dimension, or it may be incur- 
vated: so that the notion of a third dimension 
enters into our conception of a surface; for it is 
only by means of this third dimension, that we 
can distinguish surfaces into plain and curve sur- 
faces; and neither one nor the other can be con- 
ceived, without conceiving a third dimension. 

The being we have supposed having no con- 
ception of a third dimension, his visible figures 
have length and breadth indeed; but thickness 
is neither included nor excluded, being a thing 
of which he has no conception. And therefore 
visible figures, although they have length and 
breadth, as surfaces have, yet they are neither 
plain surfaces, nor curve surfaces. For a curve 
surface implies curvature in a third dimension, 
and a plane surface implies the want of cu: vature 
in a third dimension ; and such a being can con- 
ceive neither of these, because he has no concep- 
tion of a third dimension. Moreover, although 
he hath a distinct conception of the inclination 
of two lines which make an angle, yet he can 
neither conceive a plane angle, nor a spherical 
angle. Even his notion of a point is somewhat 
less determined than ours. In the motion of a 

xr o 



196 OF THE HUMAN MIND. [CHAP. 6. 

point, we exclude length, breadth, and thickness; 
he excludes length and breadth, but cannot either 
exclude or include thickness, because he hath no 
conception of it, 

Having thus settled the notions which such a 
being as we have supposed might form of mathe- 
matical points, lines, angles and figures,, it is easy 
to see, that by comparing these together, and 
reasoning about them, he might discover their 
relations, and form geom etrical conclusions, built 
upon self-evident principles. He might likewise, 
without doubt, have the same notion of numbers 
as we have, and form a system of arithmetic. It 
is not material to say in what order lie might pro- 
ceed in such discoveries, or how much time and 
pains he might employ about them ; but what 
such a being, by reason and ingenuity, without 
any materials of sensation but those of sight only, 
might discover. 

As it is more difficult to attend to a detail of 
possibilities, than of facts even of slender authori- 
ty, I shall beg leave to give an extract from the 
travels of Johannes Rudolphus Anepigraphus, 
a Rosicrucian philosopher, who having, by deep 
study of the occult sciences, acquired the art of 
transporting himself to various sublunary regions, 
and of conversing with various orders of intelli- 
gences, in the course of his adventures, became 
acquainted with an order of beings exactly such 
as I havv«5 supposed. 

How ti\ey communicate their sentiments to one 
another, an d by what means he became acquaint- 



SECT. 9.] OP SEEING. 197 

ed with their language, and was initiated into 
their philosophy, as well as of many other parti- 
culars, which might have gratified the curiosity 
of his readers, and perhaps added credibility to 
his relation, he hath not thought fit to imform us; 
these being matters proper for adepts only to 
know. 

His account of their philosophy is as follows: 
4 The Idomenians,' saith he, ' are many of 
4 them very ingenious, and much given to con- 

* templation. In arithmetic, geometry, metaphy- 
1 sics, and physics, they have most elaborate sys- 

* terns. In the two latter indeed they have had 
4 many disputes, carried on with great subtility, 
'and are divided into various sects; yet in the 

* two former there hath been no less unanimity 

* than among the human species. Their princi- 

* pies relating to numbers and arithmetic, making 
4 allowance for their notation, differ in nothing 
4 from ours ; but their geometry differs very con- 
4 siderably.' 

As our author's account of the geometry of 
the Idomenians agrees in every thing with the 
geometry of visibles, of which we have already 
given a specimen, we shall pass over it. He goes 
on thus: ' Colour, extension, and figure, are con- 
4 ceived to be the essential properties of body. 
4 A very considerable sect maintains, that colour 
4 is the essence of body. If there had been no 
4 colour, say they, there had been no perception 
1 or sensation. Colour is all that we perceive or 
4 can conceive, that is peculiar to body; exten- 
■n3 



198 OF THE HUMAN MIND. [CHAP. 6. 

* sion and figure being modes commoti to body 

* and to empty space. And if we should suppose 
6 a body to be annihilated, colour is the only thing 
' in it that can be annihilated; for its place and 
6 consequently the figure and extension of that 
'place, must remain, and cannot be imagined not 
' to exist. These philosophers hold space to be 
' the place of all bodies, immoveable and inde- 
' structible, without figure and similar in all its 
' parts, incapable of increase or diminution, yet 
'not unmeasurable: for every the last part of 
' space bears a finite ratio to the whole. So that 
' with them the whole extent of space is the com- 
1 mon and natural measure of every thing that 
' hath length and breadth, and the magnitude of 
' every body and of every figure is expressed by 
' its being such a part of the universe. In like 

* manner the common and natural measure of 

* length, is an infinite right line, which, as hath 
' been before observed, returns into itself, and 

* hath no limits, but bears a finite ratio to every 

* other line. 

* As to their natural philosophy, it is now ac- 
' knowledged by the wisest of them to have been 
' for many ages in a very low state. The philo- 
c sophers observing, that one body can differ from 
' another only in colour, figure, or magnitude, it 

* was taken for granted, that, all their particular 

* qualities must, arise from the various combina- 
6 tions of these their essential attributes. And 
' therefore it was looked upon as the end of na- 
8 tural philosophy, to show how the various com- 



SECT. 9.] OF SEEING. 199 

1 binations of these three qualities in different bo- 

* dies produced all the phenomena of nature. It 
< were endless to enumerate the various svstems 
4 that were invented with this view, and the dis- 
•putes that were carried on for ages; the follow*- 
' ers of every system exposing the weak sides of 

* other systems^ and palliating those of their, own 

* with great art. 

* At last, some free and" facetious spirits, wea- 
c ried with eternal disputation, and the labour of 
4 patching and proping weak systems, began to 

* complain' of the subtility of nature; of the infr- 
*nite changes that bodies undergo in figure,, co- 

* lour, and magnitude; and of the difficulty of 

* accounting for these appearances, making these 

* a pretence for giving up all inquiries into the 

* causes of thingSj as vain and fruitless* 

* These wits had ample matter of mirth and 
« ridicule in the systems of philosophers, and 
4 rinding it an easier task to pull down than to 

* build or support, and that every sect furnished 
« them with arms and auxiliaries- to destroy an^ 
4 other, they began to spread mightly, and went 
4 on with great success. Thus philosophy ^ave 
« way to scepticism and irony, and those systems 

* which had been the work of ages and the ad- 
« miration of the learned, became the jest of the 
'vulgar: for even the vulgar readily took part 

* in the triumph over a kind of learning which, 
« they had long suspected, because it produced 
'nothing but wrangling and altercation. The 

J w its having now acquired great reputation, and 



200 OF THE HUMAN MIND. [CHAP. 6. 

c being flushed with success, began to think the 
' triumph incomplete, until every pretence to 
'knowledge was overturned; and accordingly 
' began their attacks upon arithmetic, geometry, 
' and even upon the common notions of untaught 
' Idomenians. So difficult it hath always been, 
t (says our author) for great conquerors to know 

* where to stop.- 

* In the mean time, natural philosophy began 
'to rise from its ashes, under the direction of 

* a person of great genius, who is looked upon 
' as having had something in him above Ido- 
'menian nature. He observed, that the Ido- 
' menian faculties were certainly intended for 
■ contemplation, and that the works of nature 

* were a nobler subject to exercise them upon, 

* than the follies of systems, or the errors of the 

* learned; and being sensible of the difficulty 
' of finding out the causes of natural things, he 
' proposed, by accurate abservation of the pheno- 

* mena of nature, to find out the rules according 
' to which they happen, without inquiring into 

* the causes of those rules. In this he made con- 
f siderable progress himself, and planned out 

* much work for his followers, who call them- 
' selves inductive philosophers. The sceptics look 

* with envy upon this rising sect, as eclipsing their 
'reputation and threatening to limit their em- 
' pire ; but they are at a loss on what hand to 
1 attack it. The vulgar begin to reverence it, as 
6 producing useful discoveries. 

' It is to be observed, that every Idomenian 



SECT. 9.] OF SEEING. 201 

' firmly believes, that two or more bodies may 
1 exist in the same place. For this they have 
4 the testimony of sense, and they can no more 

* doubt of it, than they can doubt whether they 

* have any perception at all. They often see two 

* bodies meet, and coincide in the same place, and 

* separate again, without having undergone any 
1 change in their sensible qualities by this pene- 

* tration. When two bodies meet, and occupy 

* the same place, commonly one only appears in 

* that place, and the other disappears. That 

* which continues to appear is said to overcome, 
' the other to be overcome.' 

To this quality of bodies they gave a name 
which our author tells us hath no word answering 
to it in any human language. And therefore, 
after making a long apology, which I omit, he 
begs leave to call it the overcoming quality of bodies. 
He assures us, that ' the speculations which had 
4 been raised about this single quality of bodies, 

* and the hypothesis contrived to account for it, 
1 were sufficient to fill many volumes. Nor have 
' there been fewer hypothesis invented by their 
' philosophers, to account for the changes of mag- 
nitude and figure; which, in most bodies that 

* move, they perceive to be in a continual fluc- 

* tuation. The founder of the inductive sect, be- 

* lieving it to be above the reach of Idomenian 
' faculties to discover the real causes of these 
1 phenomena, applied himself to find from ob- 

* servation, by what laws they are connected to- 
'gether; and discovered many mathematical 



202 OF THE HUMAN MIND. [CHAP. 6. 

* ratios and relations concerning the motions, 

* magnitudes, figures, and overcoming quality of 
'bodies, which constant experience confirms. 

* But the oppdsers of this sect choose rather to 

* content themselves with feigned causes of these 
1 phenomena, than to acknowledge the real laws 
6 whereby they are governed, which humble their 
'pride, by being confessedly unaccountable.' 

Thus far Johannes Rudolphus Anepigraphus. 
Whether this Anepigraphus be the same who is 
recorded among the Greek alchemistical writers 
not yet published, by Borrichius, Fabricius, 
and others, I do not pretend to determine. The 
identity of their name, and the similitude of their 
studies, although no slight arguments, yet are 
not absolutely conclusive. Nor will I take upon 
me to judge of the narrative of this learned tra- 
veller by the external marks of his credibility; I 
shall confine myself to those which the critics call 
internal. It would even be of small importance 
to inquire, whether the Idomenians have a real, 
or only an ideal existence; since this is disputed 
among the learned with regard to things with 
which we are more nearly connected. The im- 
portant question is, Whether the account above 
given, is a just account of their geometry and 
philosophy. We have all the faculties which they 
have, with the addition of others which they have 
not; we may therefore form some judgment of 
their philosophy and geometry, by separating 
from all others, the perceptions we have by sight, 
and reasoning upon them. As far as I am able 



SECT. 10.] OF SEEING; 203 

to judge in this way, after a careful examination, 
their geometry must be such as Anepigraphus 
hath described. Nor does his account of their 
philosophy appear to contain any evident marks 
of imposture ; although here, no doubt, proper 
allowance is to be made for liberties which tra- 
vellers take, as well as for involuntary mistakes 
which they are apt to fall into. 



SECT. X. 

Of the parallel motion of the eyes. 

Having explained, as distinctly as we can, visible 
figure, and shewn its connexion with the things 
signified by it, it will be proper next to consider 
some phenomena of the eyes, and of vision; 
which have commonly been referred to custom, 
to anatomical or to mechanical causes; but which, 
as I conceive, must be resolved into original 
powers and principles of the human mind; and 
therefore belong properly to- the subject of this 
inquiry. 

The first is, the parallel motion of the eyes^by 
which, when one eye is turned to the right or to 
the left, upwards or downwards, or straight for- 
wards, the other always goes along with it in the 
same direction. We see plainly, when both eyes 
are open, that they are always turned the same 
way, as if both were acted upon by the same mo- 



204 OF THE- HUMAN MIND. [CHAP. 6. 

live force; and if one eye is shut, and the handi 
laid upon it, while the other turns various ways, 
we feel the eye that is shut turn at the same time, 
and that whether we will or not. What makes 
this phenomenon surprising is, that it is acknow- 
ledged by all anatomists, that the muscles which 
move the two eyes, and the nerves which serve 
these muscles, are entirely distinct- and uncon- 
nected. It would be thought very surprising 
and unaccountable, to see a man, who, from his 
birth, never moved one arm, without moving 
the other precisely in the same manner, so as to 
keep them always parallel : yet it would not be 
more difficult to find the physical cause of such 
motion of the arms, than it is to find the cause 
of the parallel motion of the eyes, which is per- 
fectly similar. 

The only cause that hath been assigned of this 
parallel motion of the eyes, is custom. We find 
by experience, it is said, when we begin to look 
at objects, that, in order to have distinct vision, 
it is necessary to turn both eyes the same way; 
therefore we soon acquire the habit of doing it 
eonstantly, and by degrees lose the power of 
doing otherwise. 

This account of the matter seems to be insuf- 
ficient; because habits are not got at once; it 
takes time to acquire and to confirm them; and 
if this motion of the eyes were got by habit, we 
should see children when they are born turn 
their eyes different ways, 'and move one without 
the other, as they do their hands or legs. I know 



S£CT. 10.] OF SEEING. 205 

some have affirmed that they are "apt to do so ; 
but I have never found it true from my own ob- 
servation, although I have taken pains to make 
observations of this kind, and have had gopd op- 
portunities. I have likewise consulted experienced 
midwives, mothers, and nurses, and found them 
agree, that they never had observed distortions 
of this kind in the eyes of children, but when 
they had reason to suspect convulsions or some 
preternatural cause. 

It seems therefore to be extremely probable, 
that, previous to custom, there is something in 
the constitution, some natural instinct which di- 
rects us to move both eyes always the same 
way. 

We know not how the mind acts upon the bo- 
dy, nor by what power the muscles are contract- 
ed and relaxed; but we see that in some of the 
voluntary, as well as in some of the involuntary 
motions, this power is so directed that many 
muscles which have no material tie or connection, 
act in concert, each of them being taught to play 
its part in exact time and measure. Nor doth a 
company of expert players in a theatrical perform- 
ance, or of excellent musicians in a concert, or 
of good dancers in a country dance, with more 
regularity and order, conspire and contribute 
their several parts, to produce one uniform effect, 
than a number of muscles do, in many of the ani- 
mal functions, and in many voluntary actions. 
Yet we see such actions no less skilfully and re- 
gularly performed in children, and in those who 



206 OF THE HUMAN MIND. [CHAP. 6-. 

know not that they have such muscles, than in 
the most skilful anatomist and physiologist. 

Who taught all the muscles that are concerned 
in sucking, in swallowing our food, in breathing, 
and in the several natural expulsions, to act their 
part in such regular order and exact measure? 
It was not custom surely. It was that same 
powerful and wise Being who made the fabric of 
the human body, and fixed the laws by which 
the mind operates upon every part of it, so that 
they may answer the purposes intended by them. 
And when we see in so many other instances, a 
system of unconnected muscles conspiring so 
wonderfully in their several functions, without 
the aid of habit, it needs not be thought strange, 
that the muscles of the eye should, without this 
aid, conspire to give that direction to the eyes, 
without which they could not answer their end. 

We see a like conspiring action in the muscles 
which contract the pupils of the two eyes; and 
in those muscles, whatever they be, by which the 
conformation of the eye is varied, according to 
the distance of objects. 

It ought however to be observed, that although 
it appears to be by natural instinct that both eyes 
are always turned the same way, there is still more 
latitude left for custom. 

What we have said of the parallel motion of 
the eyes, is not to be understood so strictly as if 
nature directed us to keep their axes always pre- 
cisely and mathematically parallel to each other. 
Indeed, although they are always nearly parallel, 



SECT. 10.] OF SEEING. 207 

they hardly ever are exactly so. When we look 
at an object, the axes of the eyes meet in that 
object; and therefore make an angle, which is 
always small, but will be greater or less, accord- 
ing as the object is nearer or more remote. Na- 
ture hath very wisely left us the power of varying 
the parallelism of our eyes a little, so that we can 
direct them to the same point, whether remote 
or near. This, no doubt, is learned by custom; 
and accordingly we see, that it is a long time be- 
fore children get this habit in perfection. 

The power of varying the parallelism of the 
eyes is naturally no more than is sufficient for 
the purpose intended by it; but by much prac- 
tice and straining, it may be increased. Accord- 
ingly we see, that some have acquired the power 
of distorting their eyes into unnatural directions, 
as others have acquired the power of distorting 
their bodies into unnatural postures. 

Those who have lost the sight of an eye, com- 
monly lose what they had got by custom, in the 
direction of their eyes, but retain what they had 
by nature; that is, although their eyes turn and 
move always together, yet when they look upon 
an object, the blind eye will often have a very 
small deviation from it; which is not perceived 
by a slight observer, but may be discerned by 
one accustomed to make exact observations jn 
these matters. 



208 OF THE HUMAN MIND. [CHAP. 6. 

SECT. XL 
Of our seeing objects erect by inverted images* 

Another phenomenon which hath perplexed 
philosophers, is our seeing objects erect, when it 
is well known that their images or pictures upon 
the tunica retina of the eye are inverted. 

The sagacious Kepler first made the noble 
discovery, That distinct but inverted pictures of 
visible objects are formed upon the retina by the 
rays of light coming from the object. The same 
great philosopher demonstrated from the princi- 
ples of optics how these pictures are formed, to 
wit, That the rays coming from any one point of 
the object, and falling upon the various parts of 
the pupil, are, by the cornea and crystalline, re- 
fracted so as to meet again in one point of the 
retina, and there paint the colour of that point of 
the object from which they come. As the rays 
from different points of the object cross each 
other before they come to the retina, the picture 
they form must be inverted: the upper part of 
the object being painted upon the lower part of 
the retina, the right side of the object upon the 
left of the retina, and so of the other parts. 

This philosopher thought that we see objects 
erect by means of these inverted pictures, for this 
reason, That as the rays from different points of 
the object cross each other, before they fall upon 



SECT. 11. J OF SEEING. 209 

the retina, we conclude that the impulse which 
we feel upon the lower part of the retina, comes 
from above; and that the impulse which we feel 
upon the higher part, comes from below. 

Des Cartes afterwards gave the same solution 
of this phenomena, and illustrated it by the judg- 
ment which we form of the position of objects 
which we feel with our arms crossed, or with two 
sticks that cross each other. 

But we cannot acquiesce in this solution.— 
First, Because it supposes our seeing things 
erect, to be a deduction of reason, drawn from 
certain premises : whereas it seems to be an im- 
mediate perception. And, secondly, Because the 
premises from which all mankind are supposed 
to draw this conclusion, never entered into the 
minds of the far greater part, but are absolutely 
unknown to them. We have no feeling or per- 
ception of the pictures upon the retina, and as 
little surely of the position of them. In order to 
see objects erect, according to the principles of 
Kepler or Des Cartes, we must previously 
know, that the rays of light come from the ob- 
ject to the eye in straight lines; we must know, 
that the rays from different points of the object 
cross one another, before they form* the pictures 
upon the retina; and lastly, we must know, that 
these pictures are really inverted. Now, al- 
though all these things are true, and known to 
philosophers, yet they are absolutely unknown to 
the far greatest part of mankind; nor is it possi- 
ble that they who are absolutely ignorant of them 



£10 OF THE HUMAN MIND. [CHAP. G. 

should reason from them, and build conclusions 
upon them. Since therefore visible objects ap- 
pear erect to the ignorant as well as to the learn- 
ed, this cannot be a conclusion drawn from pre- 
mises which never entered into the minds of the 
ignorant. We have indeed had occasion to ob- 
serve many instances of conclusions drawn, ei- 
ther by means of original principles, or by habit, 
from premises which pass through the mind 
very quickly, and which are never made the ob- 
jects of reflection; but surely no man will con- 
ceive it possible to draw conclusions from pre- 
mises- which never entered into the mind at all. 

Bishop Berkeley having justly rejected this 
solution, gives one founded upon his own prin- 
ciple; wherein he is followed by the judicious 
Dr. Smith in his Optics; and this we shall next 
explain and examine. 

That ingenious writer conceives the ideas of 
sight to be altogether unlike those of touch. And 
since the notions we have of an object by these 
different senses have no similitude, we can learn 
only by experience how one sense will be affect- 
ed, by what, in a certain manner, affects the 
other. Figure, position, and even number, in 
tangible objects, are ideas of touch; and although 
the,re is no similitude between these and the ideas 
of sight, yet we learn by experience, that a tri- 
angle affects the sight in such a manner, and that 
a square affects.it in such another manner: hence 
we judge that which affects it in the first manner, 
to be a triangle, and that which affects it in the 



SECT. 11.] OF SEEING. 211 

second, to be a square. In the same way, find- 
ing from experience, that an object in an erect 
position, affects the eye in one manner, and the 
same object in an inverted position, affects it in 
another, we learn to judge, by the manner in 
which the eye is affected, whether the object is 
erect or inverted. In a word, visible ideas, ac- 
cording to this author, are signs of the tangible; 
and the mind passeth from the sign to the thing 
signified, not by means of any similitude between 
the one and the other, nor by any natural prin- 
ciple; but by having found them constantly con- 
joined in experience, as the sounds of a language 
are with the things they signify. So that if the 
images upon the retina had been always erect, 
they would have shewn the object erect, in the 
manner as they do now that they are inverted: 
nay, if the visible idea which we now have from 
an inverted object, had been associated from the 
beginning with the erect position of that object, 
it would have signified an erect position, as readily 
as it now signifies an inverted one. And if the 
visible appearance of two shillings had been found 
connected from the beginning with the tangible 
idea of one shilling, that appearance would as 
naturally and readily have signified the unity of 
the object, as now it signifies its duplicity. 

This opinion is undoubtedly very ingenious; 
and, if it is just, serves to resolve, not only the 
phenomenon now under consideration, but like- 
wise that which we shall next consider, our seeing 
objects single with two eyes. 

o 2 



21 % OF THE HUMAN MIND. [CHAP. 6. 

It is evident, that in this solution it is suppos- 
ed, that we do not originally, and previous to ac- 
quired habits, see things either erect or inverted, 
of one figure or another, single or double, but 
learn from experience to judge of their tangible 
position, figure, and number, by certain visible 
signs. 

Indeed, it must be acknowledged to be ex* 
tremeiy difficult to distinguish the immediate and 
natural objects of sight, from the conclusions 
which we have been accustomed from infancy to 
draw from them. Bishop Berkeley was the first 
that attempted to distinguish the one from the 
other, and to trace out the boundary that divides 
them. And if, in doing so, he hath gone a little 
to the right hand or to the left, this might be ex- 
pected in a subject altogether new, and of the 
greatest subtilty. The nature of vision hath re- 
ceived great light from this distinction; and many 
phenomena in optics, which before appeared al- 
together unaccountable, have been clearly and 
distinctly resolved by it. It is natural, and al- 
most unavoidable, to one who hath made an im- 
portant discovery in philosophy, to carry it a 
little beyond its sphere, and to apply it to the re- 
solution of phenomena which do not fall within its 
province. Even the great Newton, when he had 
discovered the universal law of gravitation, and 
observed how many of the phenomena of nature 
depend upon this, and other laws of attraction 
and repulsion, could not help expressing his con- 
jecture, that all the phenomena of the material 



SEC^. 11.] OF SEEING. 213 

world depend upon attracting and repelling forces 
in the particles of matter. And I suspect that 
the ingenious Bishop of Cloyne, having found so 
many phenomena of vision reducible to the con- 
stant association of the ideas of sight and touch, 
carried this principle a little beyond its just limits. 

In order to judge, as well as we can, whether 
it is so, let us suppose such a blind man as Dr. 
Saunderson, having all the knowledge and abili- 
ties which a blind man may have, suddenly made 
to see perfectly. Let us suppose him kept from 
all opportunities of associating his ideas of sight 
with those of touch, until the former become a; 
little familiar; and the first surprise, occasioned 
by objects so new, being abated, he has time to 
canvass them, and to compare them, in his mind,, 
with the notions which he formerly had by touch, 
and in particular to compare, in his mind, that 
visible extension which his eyes present, with the 
extension in length and breadth with which he 
was before acquainted. 

Y\ r e have endeavoured to prove, that a blind 
man may form a notion of the visible extension 
and figure of bodies, from the relation which it 
bears to their tangible extension and figure. 
Much more, when this visible extension and fi- 
gure are presented to his eye, will he be able to 
compare them with tangible extension and figure, 
and to perceive, that the one has length and 
breadth as well as the other; that the one may 
be bounded by lines, cither straight or curve, as 
well as the other. And therefore, he will per- 

o 2 



214 OF THE HUMAN MIND. [CHAP. 6. 

ceive, that there may be visible as well as tangi- 
ble circles, triangles, quadrilateral and multilate- 
ral figures. And although the visible figure is 
coloured, and the tangible is not, they may, not- 
withstanding, have the same figure; as two ob- 
jects of touch may have the same figure, although 
one is hot and the other cold. 

We have demonstrated, that the properties of 
visible figures differ from those of the plain figures 
which thy represent: but it was observed at the 
same time, that when the object is so small as to be 
seen distinctly at one view, and is placed directly 
before the eye, the difference between the visible 
and the tangible figure is too small to be perceiv- 
ed by the senses. Thus, it is true, that of every 
visible triangle, the three angles are greater than 
two right angles; whereas, in a plain triangle, the 
three angles are equal to two right angles: but, 
when the visible triangle is small, its three angles 
will be so nearly equal to two right angles, that 
the sense cannot discern the difference. In like 
manner, the circumferences of unequal visible 
circles are not, but those of plain circles are, in 
the ratio of their diameters: yet in small visible 
circles, the circumferences are very nearly in the 
ratio of their diameters; and the diameter bears 
the same ratio to the circumference, as in a plain 
circle, very nearly. 

Hence it appears, that small visible figures 
(and such only can be seen distinctly at one view) 
have not only a resemblance to the plain tangi- 
ble figures which have the same name, but are to 



SECT. 11.] OF SEEING. 5215 

all sense the same. So that if Dr. Saunderson t 
had been made to see, and had attentively view- 
ed the figures of the first book of Euclid, he 
might, by thought and consideration, without 
touching them, have found out that they were 
the very figures he was before so well acquainted 
with by touch. 

When plain figures are seen obliquely, their 
visible figure differs more than the tangible; and 
the representation which is made to the eye, of 
solid figures, is still more imperfect; because 
visible extension hath not three, but two dimen- 
sions only. Yet, as it cannot be said that an ex- 
act picture of a man hath no resemblance of the 
man, or that a perspective view of a house hath 
no resemblance of the house; so it cannot be 
said, with any propriety, that the visible figure of 
a man, or of a house, hath no resemblance of the 
objects which they represent. 

Bishop Berkeley therefore proceeds upon a 
capital mistake, in supposing that there is no re- 
semblance betwixt the extension, figure, and po- 
sition which we see, and that which we perceive 
by touch. 

We may farther observe, that Bishop Berke- 
ley's system, with regard to material things, 
must have made him see this question, of the 
erect appearance of objects, in a very different 
light from that in which it appears to those who 
do not adopt his system. 

In his theory of vision, he seems indeed to al- 
low, that there is an external material world; 



216 OF THE HUMAN MIND. [CHAP. 6. 

but he believed that this external world is tangi- 
ble only, and not visible; and that the visible 
world, the proper object of sight, is not external, 
but in the mind. If this is supposed, he that 
affirms that he sees things erect and not inverted, 
affirms that there is a top and a bottom, a right 
and a left in the mind. Now, I confess I am not 
so well acquainted with the topography of the 
mind, as to be able to affix a meaning to these 
words when applied to it. 

We shall therefore allow, that if visible objects 
were not external but existed only in the mind, 
they could have no figure, or position, or exten- 
sion ; and that it would be absurd to affirm, that 
they are seen either erect or inverted; or that 
there is any resemblance between them and the 
objects of touch. But when we propose the ques- 
tion, Why objects are seen erect and not invert- 
ed? we take it for granted, that we are not in 
Bishop Berkeley's ideal world, but in that world 
which men, who yield to the dictates of common 
sense, believe themselves to inhabit. We take it 
for granted, that the objects both of sight and 
touch, are external, and have a certain figure, 
and a certain position with regard to one another, 
and with regard to our bodies, whether we per- 
ceive it or not. 

When I hold my walking-cane upright in my 
hand, and look at it, I take it for granted, that I 
see and handle the same individual object. — 
When 1 say that I feel it erect, my meaning is, 
that I feel the head directed from the horizon, 



SECT. 12.] OF SEEING. 217 

and the point directed towards it: and when I 
say that I see it erect, I mean that I see it with 
the head directed from the horizon, and the point 
towards it. I conceive the horizon as a fixed 
object both of sight and touch, w r ith relation to 
which objects are said to be high or low, erect 
or inverted: and when the question is asksd, 
Why I see the object erect and not inverted? it 
is the same, as if you should ask, Why I see it 
in that position which it really hath? or, Why the 
eye shows the real position of objects, and doth 
not show them in an inverted position, as they 
are seen by a common astronomical telescope, or 
as their pictures are seen upon the retina of an 
eye when it is dissected. 



SECT. XII. 

The same subject continued. 

It is impossible to give a satisfactory answer to 
this question, otherwise than by pointing out the 
laws of nature, which take place in vision ; for by 
these the phenomena of vision must be regulated. 
Therefore I answer, First, That by a law of 
nature the rays of light proceed from every point 
of the object to the pupil of the eye in straight 
lines. Secondly, That by the laws of nature, the 
rays coming from any one point of the object to 
the various parts of the pupil, are so refracted, as 



"218 OF THE HUMAN MIND. [CHAP. 6. 

to meet again in one point of the retina; and the 
rays from different points of the object, first cross- 
ing each other, and then proceeding to as many 
different points of the retina, form an inverted 
picture of the object. 

So far the principles of optics carry us, and 
experience further assures us, that if there is no 
such picture upon the retina, there is no vision; 
and that such as the picture on the retina is, such 
is the appearance of the object in colour and fi- 
gure, distinctness or indistinctness, brightness or 
faintness. 

It is evident, therefore, that the pictures upon 
the retina are, by the laws of nature, a mean of 
vision; but in what way they accomplish their 
end, we are totally ignorant. Philosophers con- 
ceive, that the impression made on the retina 
by the rays of light, is communicated to the op- 
tic nerve, and by the optic nerve conveyed to 
some part of the brain, by them called the senso- 
rium; and that the impression thus, conveyed to 
the sensorium is immediately perceived by the 
mind, which is supposed to reside there. But 
we know nothing of the seat of the soul: and we 
are so far from perceiving immediately what is 
transacted in the brain, that of all parts of the 
human body we know least about it. It is indeed 
very probable, that the optic nerve is an instru- 
ment of vision no less necessary than the retina; 
and that some impression is made upon it, by 
means of the pictures on the retina. But of what 
kind this impression is, we know nothing. 



SECT. 12. OF SEEING. 219 

There is not the least probability, that there is 
any picture or image of the object either in the 
optic nerve or brain. The pictures on the retina 
are formed by rays of light; and whether we 
suppose, with some, that their impulse upon the 
retina causes some vibration of the fibres of the 
optic nerve; or, with others, that it gives mo- 
tion to some subtile fluid contained in the nerye; 
neither that vibration, nor this motion, can re- 
semble the visible object which is presented to 
the mind. Nor is there any probability, that the 
mind perceives the pictures upon the retina. 
These pictures are no more objects of our per- 
ception, than the brain is, or the optic nerve. 
No man ever saw the pictures in his own eye, 
nor indeed the pictures in the eye of another, 
until it was taken out of the head, and duly pre- 
pared. 

It is very strange, that philosophers of all ages 
should have agreed in this notion, That the im- 
ages of external objects are conveyed by the or- 
gans of sense to the brain, and are there perceiv- 
ed by the mind. Nothing can be more unphilo- 
sophical. For, first, This notion hath no founda- 
tion in fact and observation. Of all the organs 
of sense, the eye only, as far as we can dis- 
cover, forms any kind of image of its object; 
and the images formed by the eye are not in 
the brain, but only in the bottom of the eye; 
nor are they at all perceived or felt by the mind. 
Secondly, It is as difficult to conceive how the 
mind perceives images on the brain, as how it 



220 QF THE HUMAN MIND. [CHAP. G. 

perceives things more distant. If any man will 
shew how the mind may perceive images in the 
brain, I will undertake to show how it may per- 
ceive the most distant objects; for if we give eyes 
to the mind, to perceive what is transacted at 
home in its dark chamber, why may we not make 
these eyes a little longer sighted? and then we 
shall have no occasion for that unphilosophical 
fiction of images in the brain. In a word, the 
manner and mechanism of the brain's perception 
is quite beyond our comprehension: and this way 
of explaining it by images in the brain, seems to 
be founded upon very gross notions of the mind 
and its operation ; as if the supposed images in 
the brain, by a kind of contact, formed similar 
impressions or images of objects upon the mind, 
of which impressions it is supposed to be con- 
scious. 

We have endeavoured to shew, throughout the 
course of this inquiry, that the impressions made 
upon the mind, by means of the five senses, have 
not the least resemblance to the objects of sense: 
and therefore, as we see no shadow of evidence, 
that there are any such images in the brain, so 
we see no purpose, in philosophy, that the sup- 
position of them can answer. Since the picture 
upon the retina, therefore, is neither itself seen 
by the mind, nor produces any impression upon 
the brain or sensorium, which is seen by the mind, 
nor makes any impression upon the mind that re- 
sembles the object, it may still be asked, How 
this picture upon the retina causes vision? 



SECT. 12.] OF SEEING. 221 

Before we answer this question, it is proper to 
observe, that in the operations of the mind, as 
well as in those of bodies, we must often be satis- 
fied with knowing that certain things are con- 
nected, and invariably follow one another, with- 
out being able to discover the chain that goes 
between them. It is to such connections that 
we give the name of laws of nature; and when we 
say that one thing produces another by a law of 
nature, this signifies no more, but that one thing, 
which we call in popular language, the cause, is 
constantly and invariably followed by another, 
which we call the effect; and that we know not 
how they are connected. Thus, we see, it is a 
fact, that bodies gravitate towards bodies; and 
that this gravitation is regulated by certain ma- 
thematical proportions, according to the distance 
of the bodies from each other, and their quantities 
of matter. Being unable to discover the cause of 
this gravitation, and presuming that it is the im- 
mediate operation, either of the Author of nature, 
or of some subordinate cause, which we have not 
hitherto been able to reach, we call it a law of 
nature. If any philosopher should hereafter be 
so happy as to discover the cause of gravitation, 
this can only be done by discovering some more 
general law of nature, of which the gravitation of 
bodies is a necessary consequence. In every 
chain of natural causes, the highest link is the 
primary law of nature, and the highest link which 
we can trace by just induction, is either this pri- 
mary law of nature, or a necessary consequence 



222 OF THE HUMAN MIND. [CHAP, (j. 

of it. To trace out the laws of nature, by induc- 
tion from the phenomena of nature, is all that 
true philosophy aims at, and all that it can ever 
reach. 

There are laws of nature by which the opera- 
tions of the mind are regulated; there are also 
laws of nature that govern the material system; 
and as the latter are the ultimate conclusions 
which the human faculties can reach in the phi- 
losophy of bodies, so the former are the ultimate 
conclusions we can reach in the philosophy of 
minds. 

To return, therefore, to the question above 
proposed, we may see, from what hath been just 
now observed, that it amounts to this, By what 
law of nature is a picture upon the retina, the 
mean or occasion of my seeing an external object, 
of the same figure and colour, in a contrary posi- 
tion, and in a certain direction from the eye? 

It will, without doubt, be allowed, that I see 
the whole object in the same manner and by the 
same law by which I see any one point of it. 
Now, I know it to be a fact, that, in direct vision, 
I see every point of the object in the direction 
of the right line that passeth from the centre of 
the eye to that point of the object: and I know 
likewise, from optics, that the ray of light that 
comes to the centre of my eye, passes on to the 
retina in the same direction. Hence it appears 
to be a fact, that every point of the object is seen 
in the direction of a right line passing from the 
picture of that point on the retina through the 



SECT. 12.] OF SEEING. 223 

centre of the eye. As this is a fact that holds 
universally and invariably, it must either be a 
law of nature, or the necessary consequence of 
some more general law of nature. And accord- 
ing to the just rules of philosophizing, we may 
hold it for a law of nature, until some more ge- 
neral law be discovered, whereof it is a necessary 
consequence, which I suspect can never be done. 
Thus we see, that the phenomena of vision, 
lead us by the hand to a law of nature, or a law 
of our constitution, of which law our seeing ob- 
jects erect by inverted images, is a necessary 
consequence. For it necessarily follows, from 
the law we have mentioned, that the object whose 
picture is lowest on the retina, must be seen in the 
highest direction from the eye; and that the object 
whose picture is on the right of the retina, must 
be seen on the left; so that if the pictures had 
been erect in the retina, we should have seen the 
object inverted. My chief intention in handling 
this question was to point out this law of nature, 
which, as it is a part of the constitution of the 
human mind, belongs properly to the subject of 
this inquiry. For this reason I shall make some 
further remarks upon it, after doing justice to 
the ingenious Dr. Porterfield, who long ago in 
the Medical Essays, or more lately in his Trea- 
tise of the Eye, pointed out, as a primary law of 
our nature, That a visible object appears in the 
direction of a right line perpendicular to the re- 
tina at that point where its image is painted. If 
Jines drawn from the centre of the eye to all parts 



22i OF THE HUMAN' MIND. [CHAP. 6. 

of the retina be perpendicular to it, as they must 
be very nearly, this coincides with the law we 
have mentioned, and is the same in other words. 
In order, therefore, that we may have a more 
distinct notion of this law of our constitution, we 
may observe, 

1. That we can give no reason why the retina 
is, of all parts of the body, the only one on which 
pictures made by the rays of light cause vision; 
and therefore we must resolve this solely into a 
law of our constitution. We may form such pic- 
tures by means of optical glasses upon the hand, 
or upon any part of the body; but they are 
Hot felt, nor do they produce any thing like 
vision. A picture upon the retina is as little felt 
as one upon the hand; but it produces vision; for 
no other reason that we know, but because it is 
destined by the wisdom of nature to this purpose. 
The vibrations of the air strike upon the eye, the 
palate, and the olfactory membrane, with the 
same force as upon the membrana tympani of the 
ear: The impression they make upon the last, 
produces the sensation of sound; but their im- 
pression upon any of the former .produces no 
sentation at all. This may be extended to all the 
senses, whereof each hath its peculiar laws, ac- 
cording to which the impressions made upon the 
organ of that sense, produce sensations or per- 
ceptions in the mind, that cannot be produced 
by impressions made upon any other organ, 

2. We may observe, that the laws of percep- 
tion, by the different senses, are very different, 



SECT. 12.] OF SEEING. 225 

not only in respect of the nature of the objects 
perceived by them, but likewise in respect of the 
notices they give us of the distance and situation 
of the object. In all of them the object is con- 
ceived to be external, and to have real existence 
independent of our perception : but in one, the 
distance, figure and situation of the object, are all 
presented to the mind ; in another, the figure and 
situation, but not the distance ; and in others, 
neither figure, situation, nor distance. In vain 
do we attempt to account for these varieties 
in the manner of perception by the different 
senses, from principles of anatomy or natural 
philosophy. They must at last be resolved into 
the will of our Maker, who intended that our 
powers of perception should have certain limits, 
and adapted the organs of perception, and the 
laws of nature by which they operate, to his wise 
purposes. 

When we hear an unusual sound, the sensation 
indeed is in the mind, but we know that there is 
something external that produced this sound. At 
the same time, our hearing does not inform us, 
whether the sounding body is near or at a dis- 
tance, in this direction or that j and therefore we 
look round to discover it. 

If any new phenomenon appears in the heavens, 
we see exactly its colour, its apparent place, mag- 
nitude, and figure, but we see not its distance. 
It may be in the atmosphere, it may be among 
the planets, or it may be in the sphere of the fix- 
ed stars, for any thing the eye can determine. 

p 



226 OF THE HUMAN MIND. [CHAP. 6. 

The testimony of the sense of touch reaches on- 
ly to objects that are contiguous to the organ, 
but with regard to them, is more precise and de- 
terminate. When we feel a body with our hand 
we know the figure, distance, and position of it, 
as well as whether it is rough or smooth, hard or 
soft, hot or cold. 

The sensations of touch, of seeing, and hearing, 
are all in the mind, and can have no existence 
but when they are perceived. How do they all 
constantly and invariably suggest the conception 
and belief of external objects, which exist whe- 
ther they are perceived or not? No philosopher 
can give any other answer to this, but that such 
is the constitution of our nature. How do we 
know, that the object of touch is at the fingers 
end, and no where else ? That the object of sight 
is in such a direction from the eye, and in no 
other, but may be at any distance ? and that the 
object of hearing may be at any distance ? and in 
any direction ? Not by custom surely ; not by 
reasoning, or comparing ideas, but by the consti- 
tution of our nature. How do we perceive visi- 
ble objects in the direction of right lines per- 
pendicular to that part of the retina on which 
the rays strike, while we do not perceive the 
objects of hearing in lines perpendicular to the 
membrana tympani, upon which the vibrations of 
the air strike ? Because such are the laws of our 
nature. How do we know the parts of our bo- 
dies affected by particular pains ? Not by expe- 
rience or by reasoning, but by the constitution 



SECT. 12.] OF SEEING. 227 

of nature. The sensation of pain, is, no doubt, 
in the mind, and cannot be said to have any re- 
lation, from its own nature, to any part of the 
body : but this sensation, by our constitution, 
gives a perception of some particular part of the 
body, whose disorder causes the uneasy sensa- 
tion. If it were not so, a man who never before 
felt either the gout or the toothache, when he is 
first seized with the gout in his toe, might mistake 
it for the toothache. 

Every sense therefore, hath its peculiar laws 
and limits, by the constitution of our nature; 
and one of the laws of sight is, that we always 
see an object in the direction of the right line, 
passing from its image on the retina through the 
centre of the eye. 

3. Perhaps some readers will imagine, that it 
is easier, and will answer the purpose as well, to 
conceive a law of nature, by which we shall al- 
ways see objects in the place in which they are, 
and in their true position, without having re- 
course to images on the retina, or to the optical 
centre of the eye. 

To this I answer, that nothing can be a law of 
nature, which is contrary to fact. The laws of 
nature, are the most general facts we can discover 
in the operations of nature. Like other facts 
they are not to be hit upon by a happy conjec- 
ture, but justly deduced from observation : Like 
other general facts, they are not to be drawn from 
a few particulars, but from a copious, patient, 
and cautious induction. That we see things al- 

p 2 



22S OF THE HUMAN MIND. [CHAP. 6. 

ways in their true place and position, is not fact ; 
and therefore it can be no law of nature. In a 
plain mirror, I see myself, and other things, in 
places very different from those they really occupy. 
And so it happens in every instance, wherein the 
rays coming from the object are either reliected 
or refracted before falling upon the eye. Those 
who know any thing of optics, know that, in all 
such cases, the object is seen in the direction of 
a line passing from the centre of the eye, to the 
point wheie the rays were last reflected or refract- 
ed ; and that upon this all the powers of the tele- 
scope and microscope depend. 

Shall we say, then, that it is a law of nature, 
that the object is seen in the direction which the 
rays have when they fall on the eye, or rather in 
the direction contrary to that of the rays when 
they fall upon the eye? No. This is not true, 
and therefore it is no law of nature. For the rays, 
from any one point of the object, come to all parts 
of the pupil; and therefore must have different 
directions : but we see the object only in one of 
these directions, to wit, in the direction of the 
rays that come to the centre of the eye. And 
this holds true, even when the rays that should 
pass through the centre are stopt, and the object 
is seen by rays that pass at a distance from the 
centre. 

Perhaps it may still be imagined, that although 
we are not made so as to see objects always in 
their true place, nor so as to see them precisely 
in the direction of the rays, when they fall upon 






SECT 12.] OF SEEING. 229 

the cornea ; yet we may be so made, as to see the 
object in the direction which the rays have when 
they fall upon the retina, after they have under- 
gone all their refractions in the eye, that is, in the 
direction in which the rays pass from the crystal- 
line to the retina. But neither is this true ; and 
consequently it is no law of our constitution. In 
order to see that it is not true, we must conceive 
all the rays that pass from the crystalline to one 
point of the retina, as forming a small cone, 
whose base is upon the point of the crystalline, 
and whose vertex is a point of the retina. It is 
evident that the rays which form the picture in 
this point, have various directions, even after they 
pass the crystalline 5 yet the object is seen only 
in one of these directions, to wit, in the direction 
of the rays that come from the centre of the eye. 
Nor is this owing to any particular virtue in the 
central rays, or in the centre itself; for the cen- 
tral rays may be stopt. When they are stopt, the 
image will be formed upon the same point of the 
retina as before, by rays that are not central, nor 
have the same direction which the central rays 
had : and in this case the object h seen in the same 
direction as before, although there are now no 
rays coming in that direction. 

From this induction we conclude, That our 
seeing an object in that particular direction in 
which we do see it, is not owing to any law of 
nature by which we are made to see it in the di- 
rection of the rays, either before the refractions 
in the eve, or after, but to a law of our nature, 

p 3 



230 OF THE HUMAN MIND. [CHAP. 6. 

by which we see the object in the direction of 
the right line that passeth from the picture of 
the object upon the retina to the centre of the 
eye. 

The facts upon which I ground this induction, 
are taken from some curious experiments of 
Scheiner, in his Fundament. Optic., quoted by Dr. 
Porterfield, and confirmed by his experience. 
I have also repeated these experiments, and found 
them to answer. As they are easily made, and 
tend to illustrate and confirm the law of nature I 
have mentioned, I shall recite them as briefly and 
distinctly as I can. 

Experiment 1. Let a very small object, such as 
the head of a pin, well illuminated, be fixed at 
such a distance from the eye, as to be beyond the 
nearest limit, and within the farthest limit of dis- 
tinct vision : For a young eye, not near sighted, 
the object may be placed at the distance of 
eighteen inches. Let the eye be kept steadily in 
one place, and take a distinct view of the object. 
We know from the principles of optics, that the 
rays from any one point of this object, whether 
they pass through the centre of the eye, or at any 
distance from the centre which the breadth of 
the pupil will permit, do all unite again in one 
point of the retina. We know also, that these 
rays have different directions, both before they 
fall upon the eye, and after they pass through the 
crystalline. 

Now, we can see the object by any one small 
parcel of these rays, excluding the rest, by look- 



SECT. 12.] OF SEEING. 231 

ing through a small pin-hole in a card. Moving 
this pin-hole over the various parts of the pupil, 
we can see the object, first by the rays that pass 
above the centre of the eye, then by the central 
rays, then by the rays that pass below the centre, 
and in like manner by the rays that pass on the 
right and left of the centre. Thus, we view this 
object, successively, by rays that are central, and 
by rays that are not central; by rays that have, 
different directions, and are variously inclined to 
each other, both when they fall upon the cornea, 
and when they fall upon the retina; but always 
by rays which fall upon the same point of the re- 
tina. And what is the event? It is this, that the 
object is seen in the same individual direction, 
whether seen by all these rays together, or by 
any one parcel of them. 

Experiment %. Let the object above mentioned 
be now placed within the nearest limit of distinct 
vision, that is, for an eye that is not near-sighted, 
at the distance of four or five inches. We know, 
that in this case, the rays coming from one point 
of the object, do not meet in one point of the re- 
tina, but spread over a small circular spot of it; 
the central rays occupying the centre of this 
circle, the rajs that pass above the centre occu- 
pying the upper part of the circular spot, and so 
of the rest. And we know that the object is in 
this case seen confused, every point of it being 
seen, not in one, but in various directions. To 
remedy this confusion, we look at the object 
through the pin-hole, and while we move the pin- 



232 OF THE HUMAN MIND. [CHAP. 6. 

hole over the various parts of the pupil, the ob- 
ject does not keep its place, but seems to move in 
a contrary direction. 

It is here to be observed, that when the pin- 
hole is carried upwards over the pupil, the pic- 
ture of the object is carried upwards upon the 
retina, and the object at the same time seems to 
move downwards, so as to be always in the right 
line passing from the picture through the centre 
of the eye. It is likewise to be observed, that 
the rays which form the upper and the lower pic- 
tures upon the retina, do not cross each other as 
in ordinary vision; yet still the higher picture 
shows the object lower, and the lower picture 
shews the object higher, in the same manner as 
when the rays cross each other. Whence we may 
observe, by the way, that this phenomenon of our 
seeing objects in a position contrary to that of 
their pictures upon the retina, does not depend 
upon the crossing of the rays, as Kepler and Des 
Cartes conceived. 

Experiment 3. Other things remaining as in 
the last experiment, make three pin-holes in a 
straight line, so near, that the rays coming from 
the object through all the holes, may enter the 
pupil at the same time. In this case we have a 
very curious phenomenon; for the object is seen 
triple with one eye. And if you make more holes 
"within the breadth of the pupil, you will see as 
many objects as there are holes. However, we 
shall suppose them only three; one on the right, 1 
one in the middle, and one on the left; in which 



SECT. 12.] OF SEEING. 838 

case, you see three objects standing in a line from 
right to left. 

It is here to be observed, that there are three 
pictures on the retina-, that on the left being 
formed by the rays which pass on the left of the 
eye's centre; the middle picture being formed 
by the central rays, and the right hand picture 
by the rays which pass on the right of the eye's 
centre. It is further to be observed, that the 
object which appears on the right, is not that 
which is seen through the hole on the right, but 
that which is seen through the hole on the left; 
and in like manner, the left hand object is seen 
through the hole on the right, as is easily proved 
by covering the holes successively. So that, 
whatever is the direction of the rays which form 
the right hand and left hand pictures, still the 
right hand picture shews a left hand object, and 
the left hand picture shews a right hand object. 

Experiment 4. It is easy to see how the two 
last experiments may be varied, by placing the 
object beyond the farthest limit of distinct vision. 
In order to make this experiment, I looked at a 
candle at the distance often feet, and put the eye 
of my spectacles behind the card, that the rays 
from the same point of the object might meet, 
and cross each other, before they reached the re- 
tina. In this case, as in the former, the candle 
seen triple through the three pin-holes; but 
the candle on the right, was seen through the 
hole on the right; and, on the contrary, the left 
hand candle was. seen through the hole on the 



234 OF THE HUMAN MIND. [CHAP. 6. 

left. In this experiment, it is evident from the 
principles of optics, that the rays forming the 
several pictures on the retina, cross each other 
a little before they reach the retina ; and there- 
fore the left hand picture is formed by the rays 
which pass through the hole on the right; so that 
the position of the pictures is contrary to that 
of the holes by which they are formed ; and 
therefore is also contrary to that of their objects, 
as we have found it to be in the former experi- 
ments. 

These experiments exhibit several uncommon 
phenomena, that regard the apparent place, and 
the direction of visible objects from the eye; 
phenomena that seem to be most contrary to the 
common rules of vision. When we look at the 
same time through three holes that are in a right 
line, and at certain distances from each other, 
we expect that the objects seen through them 
should really be, and should appear to be, at a 
distance from each other : Yet, by the first ex- 
periment, we may, through three such holes, see 
the same object, and the same point of that ob- 
ject ; and through all the three it appears in the 
same individual place and direction. 

Yv T hen the rays of light come from the object 
in right lines to the eye, without any reflection, 
inflection, or refraction, we expect that the ob- 
ject should appear in its real and proper direction 
from the eye ; and so it commonly does : But in 
the second, third, and fourth experiments, we see 
the object in a direction which is not its true and 



SECT. 12.] OF SEEfNG. 235 

real direction from the eye, although the rays 
come from the object to the eye, without any in- 
flection, reflection, or refraction. 

When both the object and the eye are fixed 
without the least motion, and the medium un- 
changed, we expect that the object should ap- 
pear to rest, and keep the same place : Yet in 
the second and fourth experiments, when both 
the eye and the object are at rest, and the medi- 
um unchanged, we make the object appear to 
move upwards or downwards, or in any direction 
we please. 

"When we look at the same time, and with the 
same eye, through holes that stand in a line from 
right to left, we expect, that the object seen 
through the left hand hole, should appear on the 
left, and the object seen through the right hand 
hole, should appear on the right : Yet in the third 
experiment, we find the direct contrary. 

Although many instances occur in seeing the 
same object double with two eyes, we always ex- 
pect that it should appear single when seen only 
by one eye : Yet in the second and fourth experi- 
ment, we have instances wherein the same ob- 
ject may appear double, triple, or quadruple, to 
one eye, without the help of a polyhedron or mul- 
tiplying glass. 

All these extraordinary phenomena, regarding 
the direction of visible objects from the eye, as 
well as those that are common and ordinary, lead 
us to that law of nature which I have mentioned, 
and are the necessary consequences of it. And, 



233 OF THE HUMAN MIND. [cHAI\ G, 

ps there is no probability that we shall ever be 
able to give a reason why pictures upon the retina 
make us see external objects, any more than pic- 
tures upon the hand or upon the cheek ; or, that 
we shall ever be able to give a mson, why we 
pee the object in the direction of a line passing 
from its picture through the centre of the eye, 
?ather than in any other direction : I am there- 
fore apt to look upon this law as a primary law of 
our constitution. 

To prevent being misunderstood, I beg the 
reader to observe, that I do not mean to affirm, 
that the picture upon the retina will make us see 
an object in the direction mentioned, or in any di- 
rection, unless the optic nerve, and the other more 
jmmediate instruments of vision, be sound, and 
perform their function. We know not well what 
is the office of the optic nerve, nor in what man- 
ner it performs that office ; but that it hath some 
part in the faculty of seeing, seems to be certain; 
because in an amaurosis, which is believed to be 
a disorder of the optic nerve, the pictures on the 
retina are clear and distinct, and vet there is no 
vision. 

We know still less of the use and function of 
^he chorid membrane ; but it seems likewise to 
be necessary to vision : for it is well known, that 
pictures upon that part of the retina where it is 
not covered by the chond, I mean at the entrance 
of the optic nerve, produce no vision, any more 
than a picture upon the hand. We acknowledge, 
therefore, that the retina is not the last and most 



SECT. 12.] OF SEEING. £o? 

immediate instrument of the mind in vision.— 
There are other material organs, whose operation 
is necessary to seeing, even after the pictures up- 
on the retina are formed. If ever we come to 
know the structure and use of the chorid mem- 
brane, the optic nerve, and the brain, and what 
impressions are made upon them by means of 
the pictures on the retina, some more links of the 
chain may be brought within our view, and a 
more general law of vision discovered : but while 
we know so little of the nature and office of these 
more immediate instruments of vision, it seems to 
be impossible to trace its laws beyond the pictures 
upon the retina. 

Neither do I pretend to say, that there may 
not be diseases of the eye, or accidents, which 
may occasion our seeing objects in a direction 
somewhat different from that mentioned above. 
I shall beg leave to mention one instance of this 
kind that concerns myself. 

In May 176 3, being occupied in making an 
exact meridian, in order to observe the transit 
of Venus, I rashly directed to tire sun, by my 
right eye, the cross hairs of a small telescope. I 
had often done the like in my younger days with 
impunity ; but I suffered by it at last, which I 
mention as a warning to others. 

I soon observed a remarkable dimness in that 
eye; and for many weeks, when I was in the dark, 
or shut my eyes, there appeared before the right 
eye a lucid spot, which trembled much like the 
image of the sun seen by reflection from water.— 



23S OF THE HUMAN MIND. [CHAP. 6. 

This appearance grew fainter, and less frequent, 
by degrees ; so that now there are seldom any 
remains of it. But some other very sensible ef- 
fects of this hurt still remain. For, first, The 
sight of the right eye continues to be more dim 
than that of the left. Secondly, The nearest 
limit of distinct vision is more remote in the right 
eye than in the other ; although, before the time 
mentioned, they were equal in both these re- 
spects, as I had found by many trials. But, 
thirdly, what I chiefly intended to mention, is, 
That a straight line, in some circumstances, ap- 
pears to the right eye to have a curvature in it. 
Thus, when I look upon a music-book, and shut- 
ting my left eye, direct the right to a point of the 
middle line of the five which compose the staff of 
music ; the middle line appears dim, indeed, at 
the point to which the eye is directed, but 
straight ; at the same time the two line's above it, 
and the two below it, appear to be bent outwards, 
and to be more distant from each other, and from 
the middle line, than at other parts of the staff 
to which the eye is not directed. Fourthly, Al- 
though I have repeated this experiment times in- 
numerable within these sixteen months, I do not 
find that custom and experience takes away this 
appearance of curvature in straight lines. Lastly, 
This appearance of curvature is perceptible when 
I look with the right eye only, but not when I 
look with both eyes ; yet I see better with both 
eyes together, than even with the left eye alone. 
1 have related this fact minutely as it is, with- 



SECT 15.] OF SEEING. 239 

out regard to any hypothesis; because I think 
such uncommon facts deserve to be recorded. I 
shall leave it to others to conjecture the cause of 
this appearance. To me it seems most probable, 
that a small part of the retina towards the centre 
is shrunk, and that thereby the contiguous parts 
are drawn nearer to the centre, and to one ano- 
ther, than they were before ; and that objects 
whose images fall on these parts, appear at that 
distance from each other which corresponds, not 
to the interval of the parts in their present preter- 
natural contraction, but to their interval in their 
natural and sound state. 



SECT. XIII. 

Of seeing objects single with two eyes. 

Another phenomenon of vision which deserves 
attention, is our seeing objects single with two 
eyes. There are two pictures of the object, one 
on each retina ; and each picture by itself makes 
us see an object in a certain direction from the 
eye; yet both together commonly make us see 
only one object. All the accounts or solutions of 
this phenomenon given by anatomists and philo- 
sophers, seem to be unsatisfactory. I shall pass 
over the opinions of Galen, of Gassendus, of 
Baptlsta Porta, and of Rohault. The reader 



£1<0 OF THE HUMAN MIND [CHAP. 6. 

may see these examined and refuted by Dr. 
Porterfield. I shall examine Dr. Porterfield's 
own opinion, Bishop Berkeley's, and some 
others. But it will be necessary first to ascertain 
the facts; for if we mistake the phenomena of 
single and double vision, it is ten to one but this 
mistake will lead us wrong in assigning the cause?. 
This likewise we ought carefully to attend to, 
which is acknowledged in theory by all who have 
any true judgment or just taste in inquiries of 
this nature, but is xery often overlooked in 
practice, namely, That in the solution of natural 
phenomena, all the length that the human facul- 
ties can carry us is only this, that from particu- 
lar phenomena, we may, by induction, trace out 
general phenomena, of which all the particular 
ones are necessary consequences. And when 
we have arrived at the most general pheno- 
mena we can reach, there we must stop. If it 
is asked, Why such a body gravitates towards 
the earth ? all the answer that can be given, is, 
Because all bodies gravitate towards the earth. — 
This is resolving a particular phenomenon into 
a general one. If it should again be asked, 
Why do all bodies gravitate towards the earth ? 
we can give no other solution of this phenome- 
non, but that all bodies whatsoever gravitate to- 
wards each other. This is resolving a general 
phenomenon into a more general one. If it 
should be asked, Why all bodies gravitate to one 
another? we cannot tell ; but if we could tell, it 
could only be by resolving this universal gravita- 



SECT. 13.] OF SEEING. 241 

tion of bodies into some other phenomenon stilj 
more general, and of which the gravitation of all 
bodies is a particular instance. The most general 
phenomena we can reach, are what we call laws 
of nature. So that the laws of nature are nothing 
else but the most general facts relating to the 
operations of nature, which include a great many- 
particular facts under them. And if in any case 
we should give the name of a law of nature to a 
general phenomenon, which human industry- 
shall afterwards trace to one more general, there 
is no great harm done. The most general as- 
sumes the name of a law of nature when it is dis- 
covered ; and the less general is contained and 
comprehended in it. Having premised these 
things, we proceed to consider the phenomena of 
single and double vision, in order to discover some 
general principle to which they all lead, and of 
which they are the necessary consequences. If 
we can discover any such general principle, it must 
either be a law of nature, or the necessary conse- 
quence of some law of nature ; and its authority 
will be equal, whether it is the first or the last. 

1. We find, that when the eyes are sound and 
perfect, and the axes of both directed to one 
point, an object placed in that point is seen single; 
and here we observe, that in this case the two 
pictures which show the object single, are in the 
centres of the retina. When two pictures of a 
small object are formed upon points of the retina, 
if they show the object single, we shall, for the 
sake of perspicuity, call such two points of the re- 
el 



242 OF THE HUMAN MIND. [CHAP. 6. 

Una, corresponding points ; and where the object is 
seen double, we shall call the points of the retina 
on which the pictures are formed, points that do 
not correspond. Now, in this first phenomenon it 
is evident, that the two centres of the retina are 
corresponding points. 

2. Supposing the same things as in the last 
phenomenon, other objects at the same distance 
from the eyes as that to which their axes are di- 
rected, do also appear single. Thus if I direct 
my eyes to a candle placed at the distance of ten 
feet; and, while I look at this candle, another 
stand at the same distance from my eyes within 
the field of vision ; I can, while I look at the first 
candle, attend to the appearance which the se- 
cond makes to the eye ; and I find that in this 
case it always appears single. It is here to be 
observed, that the pictures of the second candle 
do not fall upon the centres of the retince, but 
they both fail upon the same side of the centres, 
that is, both to the right, or both to the left, and 
both are at the same distance from the centres. — 
This might easily be demonstrated from' the prin- 
ciples of optics. Hence it appears, that in this 
second phenomenon of single vision, the corre- 
sponding points are points of the two retina?, which 
are similarly situate with respect to the two 
centres, being both upon the same side of the 
centre, and at the same distance from it. It ap- 
pears likewise from this phenomenon, that every 
point in one retina corresponds with that which is 
similarly situate in the other. 



SECT. 13.] OF SEEING. 248 

3. Supposing still the same things, objects 
which are much nearer to the eyes, or much more 
distant from them, than that to which the two 
eyes are directed, appear double. Thus, if the 
candle is placed at the distance of ten feet, and 
I hold my finger at arms length between my eyes 
and the candle ; when I look at the candle, I 
see my finger double ; and when I look at my 
finger, I see the candle double : And the same 
thing happens with regard to all other objects at 
like distances, which fall within the sphere of 
vision. In this phenomenon, it is evident to 
those who understand the principles of optics, 
that the pictures of the objects which are seen 
double, do not fall upon points of the rettncB 
which are similarly situate, but that the pictures 
of the objects seen single do fall upon points si- 
milarly situate. Whence we infer, that as the 
points of the two retina?, which are similarly si- 
tuate with regard to the centres, do correspond, 
so those which are dissimilarly situate do not cor- 
respond. 

4. It is to be observed, that although, in such 
cases as are mentioned in the last phenomenon, 
we have been accustomed from infancy to see 
objects double which we know to be single ; yet 
custom, and experience of the unity of the ob- 
ject, never take away this appearance of dupli- 
city. 

5. It may however be remarked, that the cus- 
tom of attending to visible appearances has a 
considerable effect, and makes the phenomenon 

q 2 



244 OF THE HUMAN MIND. [CHAP. 6\ 

of double vision to be more or less observed and 
remembered. Thus you may find a man that 
can say with a good conscience, that he never 
saw things double all his life ; yet this very man, 
put in the situation above mentioned, with his 
finger between him and the candle, and desired 
to attend to the appearance of the object which 
he does not look at, will upon the first trial, see 
the candle double, when he looks at his finger ; 
and his finger double, when he looks at the can- 
dle. Does he now see otherwise than he saw be- 
fore? No, surely; but he now attends to what 
he never attended to before. The same double 
appearance of an object hath been a thousand 
times presented to his eye before now ; but he 
did not attend to it ; and so it is as little an ob- 
ject of his reflection and memory as if it had 
never happened. 

When we look at an object, the circumjacent 
objects may be seen at the same time, although 
more obscurely and indistinctly : for the eye hath 
a considerable field of vision, which it takes in at 
once. But we attend only to the object we look 
at. The other objects which fall within the field 
of vision, are not attended to ; and therefore are 
as if they were not seen. If any of them draws 
our attention, it naturally draws the eyes at the 
same time ; for in the common course of life, the 
eyes always follow the attention : or if, at any 
time, in a reverie, they are separated from it, we 
hardly at that time see what is directly before us c 
Hence we may see the reason, why the man we 



SECT. 13.] OF SEEING. 245 

are speaking of thinks that he never before saw 
an object double. When he looks at any object, 
he sees it single, and takes no notice of othe r 
visible objects at that time, whether they appear 
single or double. If any of them draws his at- 
tention, it draws his eyes at the same time ; and 
as soon as the eyes are turned towards it, it ap- 
pears single. But in order to see things double, 
at least in order to have any reflection or remem- 
brance that he did so, it is necessary that he 
should look at one object, and at the same time 
attend to the faint appearance of other objects 
which are within' the field of vision. This is a 
practice which perhaps he never used, nor at- 
tempted ; and therefore he does not recollect that 
ever he saw an object double. But when he is 
'put upon giving this attention, he immediately 
sees objects double in the*same manner, and with 
the very same circumstances, as they who have 
been accustomed, for the greatest part of their 
lives, to give this attention. 

There are many phenomena of a similar na- 
ture, which shew, that the mind may not attend 
to, and thereby, in some sort, not perceive, objects 
that strike the senses. I had occasion to mention 
several instances of this in the second chapter; 
and I have been assured, by peisons of the best 
skill in music, that in hearing a tune upon the 
harpsichord, when they give attention to the 
treble, they do not hear the bass ; and when they 
attend to the bass, they do not perceive the air 
of the treble. Some persons are so near-sighted, 



246 OF THE HUMAN MIND, [CHAP. 6. 

that, in reading, they hold the book to one eye, 
while the other is directed to other objects. 
Such persons acquire the habit of attending in 
this case to the objects of one eye, while they give 
no attention to those of the other. 

6. It is observable that in all cases wherein 
we see an object double, the two appearances 
have a certain position with regard to one ano- 
ther, and a certain apparent or angular distance. 
This apparent distance is greater or less in differ- 
ent circumstances ; but in the same circumstan- 
ces, it is always the same, not only to the same, 
but to different persons. 

Thus, the experiment above mentioned, if 
twenty different persons, who see perfectly with 
both eyes, shall place their finger and the candle 
at the distances above expressed, and hold their 
heads upright; looking at the finger, they will 
see two candles, one on the right, another on the 
left. That which is seen on the right, is seen by 
the right eye, and that which is seen on the left, 
by the left eye ; and they will see them at the 
same apparent distance from each other. If again 
they look at the candle, they will see two fingers, 
one on the right and the other on the left ; and 
all will see them at the same apparent distance ; 
the finger towards the left being seen by the right 
eye, and the other by the left. If the head is 
laid horizontally to one side, other circumstances 
remaining the same, one appearance of the object 
seen double, will be directly above the other. — : 
In a word, vary the circumstances as you please, 



SECT. IS.] OF SEEING. 247 

and the appearances are varied to all the specta- 
tors in one and the same manner. 

7. Having made many experiments in order 
to ascertain the apparent distance of the two ap- 
pearances of an object seen double, I have found 
that in all cases this apparent distance is propor- 
tioned to the distance between the point of the 
retina, where the picture is made in one eye, and 
the point which is situated similarly to that on 
which the picture is made on the other eye. So 
that as the apparent distance of two objects seen 
with one eye, is proportioned to the arch of the 
'retina, which lies between their pictures : in like 
manner, when an object is seen double with the 
two eyes, the apparent distance of the two appear- 
ances is proportioned to the arch of either retina, 
which lies between the picture in that retina, and 
the point corresponding to that of the picture in 
the other retina. 

8. As in certain circumstances we invariably 
see one object appear double, so in others we as 
invariably see two objects unite into one; and, 
in appearance, lose their duplicity. This is evi- 
dent in the appearance of the binocular telescope. 
And the same thing happens when any two simi- 
lar tubes are applied to the two eyes in a parallel 
direction; for in this, case we see only one tube. 
And if two shillings are placed at the extremities 
of the two tubes, one exactly in the axis of one 
eye, and the other at the axis of the other eye, 
we shall see but one shilling. If two pieces of 
coin, or other bodies, of different colour, and a 



MS OF THE HUMAN MIND. [CHAP. 6. 

different figure, be properly placed, in the two axes 
of the eyes, and at the extremities of the tubes, we 
shall see both the bodies in one and the same place, 
each as it were spread over the other, without hid- 
ing it ; and the colour will be that which is com- 
pounded of the two colours. 

9. From these phenomena, and from all the 
trials I have been able to make, it appears evi- 
dently, that in perfect human eyes, the centres of 
the tvforetince correspond and harmonize with one 
another; and that every other point in one retina, 
doth correspond and harmonize with the point 
which is similarly situate in the other ; in such 
manner, that pictures falling on the correspond- 
ing points of the two retinae, show only one ob- 
ject, even when there are really two : and pictures 
falling upon points of the retinae which do not 
correspond, shew us two visible appearances, al- 
though there be but one object. So that pic- 
tures, upon corresponding points of the two reti- 
nce, present the same appearance to the mind as 
if they had both fallen upon the same point 
of one retina ; and pictures upon points of the 
two retinae, which do not correspond, present to 
the mind the same apparent distance and posi- 
tion of two objects, as if .one of those pictures 
"was carried to the point corresponding to it in 
the other retina. This relation and sympathy be- 
tween corresponding points of the two retince, I 
do not advance as ah hypothesis, but as a gene- 
ral fact or phenomenon of vision. All the phe- 
nomena before mentioned, of single or double 



SECT. 13.J OF SEEING. 24$ 

vision lead to it, and are necessary consequences 
of it. It holds true invariably in all perfect hu- 
man eyes, as far as I am able to collect from innu- 
merable trials of various kinds made upon my own 
eyes, and many made by others at my desire. — 
Most of the hypotheses that have been contrived 
to resolve the phenomena of single and double 
vision, suppose this general fact, while their au- 
thors were not aware of it. Sir Isaac Newton, 
who was too judicious a philosopher, and too ac- 
curate an observer, to have offered even a con- 
jecture which did not tally with the facts that had 
fallen under his observation, proposes a query 
with respect to the cause of it, Optics, guer. 15. 
The judicious Dr. Smith, in his Optics, lib. 9. 
§ 137. hath confirmed the truth of this generaL 
phenomenon from his own experience, not only 
as to the apparent unity of objects whose pictures 
fall upon the corresponding points of the retina?, 
but also as to the apparent distance of the two 
appearances of the same object when seen double. 
This general phenomenon appears therefore to 
be founded upon a very full induction, which is 
all the evidence we can have for a fact of this na- 
ture. Before we make an end of this subject, it 
will be proper to inquire, first, Whether those 
animals whose eyes have an adverse position in 
their heads, and look contrary ways, have such 
corresponding points in their retinco? Secondly, 
What is the position of the corresponding points 
in imperfect human eyes, I mean in those that 
-squint ? And, in the last place, Whether this bar- 



&50 OF THE HUMAN MIND. [CHAP. 6. 

mony of the corresponding points in the retinae, 
be natural and original, or the effect of custom ? 
And if it is original, Whether it can be accounted 
for by any of the laws of nature already discover- 
ed ? or whether it is itself to be looked upon as a 
Lw of nature, and a part of the human constitu- 
tion ? 



SECT. XIV. 

Of the laws of vision in bride animals. 

It is the intention of nature, in giving eyes to 
animals, that they may perceive the situation of 
visible objects, or the direction in which they are 
placed : it is probable, therefore, that, in ordinary 
cases, every animal, whether it has many eyes or 
i'ew, whether of one structure or of another, sees 
objects single, and in their true and proper direc- 
tion. And since there is a prodigious variety in 
the structure, the motions, and the number of 
eyes in different animals and instincts, it is pro- 
bable that the laws by which vision is regulated, 
are not the same in all, but various, adapted to 
the eyes which nature hath given them. 

Mankind naturally turn their eyes always the 
same way, so that the axes of the two eyes meet 
in one point. They naturally attend to, or look 
at that object only which is placed in the point 
where the axes meet. And whether the object 
be more or less distant, the configuration of the 



SECT. 14.] OF SEEING. 251 

eye is adapted to the distance of the object, so as 
to form a distinct picture of it. 

When we use our eyes in this natural way, the 
two pictures of the object we look at, are formed 
upon the centres of the two retina? ; and the two 
pictures of any contiguous object are formed upon 
the points of the re tince which are similarly situ- 
ate with regard to the centres. Therefore, in or- 
der to our seeing objects single, and in their 
proper direction, with two eyes, it is sufficient 
that we be so constituted, that objects whose pic- 
tures are formed upon the centres of the two re- 
tince, or upon points similarly situated with regard 
to these centres, shall be seen in the same visible 
place. And this is the constitution which nature 
hath actually given to human eyes. 

When we distort our eyes from their parallel 
direction, which is an unnatural motion, but may 
be learned by practice ; or when we direct the 
a?tes of the two eyes to one point, and at the same 
time direct our attention to some visible object 
much nearer or much more distant than that 
point, which is also unnatural, yet may be learn- 
ed ; in these cases, and in these only, we see one 
object double, or two objects confounded in one. 
In these cases, the two pictures of the same object 
are formed upon points of the reiince which are 
not similarly situate, and so the object is seen 
double ; or the two pictures of different objects 
are formed upon points of the retina? which are 
similarly situate, and so the two objects are seen 
confounded in one place. 



252 OF THE HUMAN MIND. [CHAP. 6r 

Thus it appears, that the laws of vision in the 
human constitution are wisely adapted to the na- 
tural use of human eyes, but not to that use of 
them which is unnatural. We see objects truly 
when we use our eyes in the natural way; but 
have false appearances presented to us when we 
use them in a way that is unnatural. We may 
reasonably think, that the case is the same with 
other animals. But is it not unreasonable to think, 
that those animals which naturally turn one eye 
towards one object, and another eye towards ano- 
ther object, must thereby have such false appear, 
ances presented to them, as we have when we do 
so against nature? 

Many animals have their eyes by nature placed 
adverse and immoveable, the axes of the two eyes 
being always directed to opposite points. Do 
objects painted on the centres of the two retinas 
appear to such animals as they do to human eyes, 
in one and the same visible place ? I think it is 
highly probable they do not; and that they ap- 
pear, as they really are, in opposite places. 

If we judge from analogy in this case, it will 
lead us to think that there is a certain correspond- 
ence between points of the two retinae in such 
animals, but of a different kind from that which 
we have found in human eyes, The centre of 
one retina will correspond with the centre of the 
other, in such manner that the objects whose 
pictures are formed upon these corresponding 
pointt, shall appeor not to be in the same place, 
as in human eyes, but in opposite places. And 



SECT. 14.] OF SEEING. 253 

in the same manner will the superior part of one 
retina correspond with the inferior part of the 
other, and the anterior part of one with the pos- 
terior part of the other. 

Some animals, by nature, turn their eyes with 
equal facility, either the same way, or different 
ways, as we turn our hands and arms. Have 
such animals corresponding points in their retbuje* 
and points which do not correspond as the hu- 
man kind has ? I think it is probable that they 
have not ; because such a constitution in them 
could serve no other purpose but to exhibit false 
appearances. 

If we judge from analogy, it will lead us to 
think, that as such animals move their eyes in a 
manner similar to that in which we move our 
arms, they have an immediate and natural per- 
ception of the direction they give to their eyes, 
as we have of the direction we give to our arms ; 
and perceive the situation of visible objects by 
their eyes, in a manner similar to that in which 
we perceive the situation of tangible objects with 
our hands. 

We cannot teach brute animals to use their 
eyes in any other way than in that which nature 
hath taught them ; nor can we teach them to 
communicate to us the appearances which visible 
objects make to them, either in ordinary or in 
extraordinary cases. We have not therefore the 
same means of discovering the laws of vision in 
them, as in our own kind, but must satisfy our- 
selves with probable conjectures: and what, we 



254 OF THE HUMAN MIND. [CHAP. 6. 

have said upon this subject, is chiefly intended to 
show, that animals to which nature hath given eyes 
differing in their number, in their position, and in 
their natural motions, may very probably be sub- 
jected to different laws of vision, adapted to the 
peculiarities of their organs of vision. 



SECT. XV. 

Squinting considered hypothetically. 

Whether there be corresponding points in the 
retina? of those who have an involuntary squint? 
and if there are, whether they be situate in the 
same manner as in those who have no squint ? 
are not questions of mere curiosity. They are 
of real importance to the physician who attempts 
the cure of a squint, and to the patient who sub- 
mits to the cure. After so much has been said of 
the strabismus , or squint, both by medical and by 
optical writers, one might expect to find abun- 
dance of facts for determining these questions. 
Yet I confess I have been disappointed in this ex- 
pectation, after taking some pains both to make 
observations, and to collect those which have been 
made by others. 

Nor will this appear very strange, if we con- 
sider, that, to make the observations which are 
necessary for determining these questions, know- 



SECT. 15.] OF SEEfNG. Q55 

ledge of the principles of optics, and of the law of 
vision, must concur with opportunities rarely to be 
met with. 

Of those who squint, the far greater part have 
no distinct vision with one eye. When this is the 
case, it is impossible, and indeed of no importance, 
to determine the situation of the corresponding 
points. When both eyes are good, they common- 
ly differ so much in their direction, that the same 
object cannot be seen by both at the same time; 
and in this case it will be very difficult to deter- 
mine the situation of the corresponding points ; 
or such persons will probably attend only to the 
objects of one eye, and the objects of the other 
will be as little regarded as if they were not seen. 

We have before observed, that when we look 
at a near object, and attend to it, we do not per- 
ceive the double appearance of more distant ob- 
jects, even when they are in the same direction, 
and are presented to ihe eye at the same time. 
It is probable that a squinting person, when he 
attends to the objects of one eye, will, in like 
manner, have his attention totally diverted from 
the objects of the other; and that he will per- 
ceive them as little as we perceive the double 
appearances of objects when we use our eyes in 
the natural way. Such a person, therefore, un- 
less he is so much a philosopher as to have ac- 
quired the habit of attending very accurately to 
the visible appearances of objects, and even of 
objects which he does not look at, will not be 
able to give any light to the questions now under 
consideration. 



256 OF THE HUMAN MIND. [CHAP. 6. 

It is very probable that hares, rabbits, birds, 
and fishes, whose eyes are fixed in an adverse po- 
sition, have the natural faculty of attending at 
the same time to visible objects placed in differ- 
ent, and even in contrary directions ; because, 
without this faculty, they could not have those 
advantages from the contrary direction of their 
eyes, which nature seems to have intended. But 
it is not probable that those who squint have any 
such natural faculty ; because we find no such fa- 
culty in the rest of the species. We naturally 
attend to objects placed* in the point where the 
axes of the two eyes meet, and to them only. 
To give attention to an object in a different di- 
rection is unnatural, and not to be learned with- 
out pains and practice. 

A very convincing proof of this may be drawn 
from a fact now well known to philosophers : 
when one eye is shut, there is a certain space 
within the field of vision, where we can see no- 
thing at all ; the space which is directed opposed 
to that part of the bottom of the eye where the 
optic nerve enters. This defect of sight, in one 
part of the eye, is common to all human eyes, 
and hath been so from the beginning of the 
world ; yet it was never known until the sagacity 
of the Abbe Mariotte discovered it in the last 
century. And now when it is known, it cannot 
be perceived, but by means of some particular 
experiments, which require care and attention to 
make them succeed. 

What is the reason that so remarkable a defect 
of sight, so common to all mankind, was so long 



SECT. 15.] OF SEEING. 257 

unknown, and is now perceived with so'much diffi- 
culty ? It is surely this, That the defect is at some 
distance from the axis of the eye, and consequent- 
ly in a part of the field of vision to which we never 
attend naturally, and to which we cannot attend 
at all, without the aid of some particular circum- 
stances. 

From what we have said, it appears, that, to 
determine the situation of the corresponding 
points in the eyes of those who squint, is impos- 
sible if they do not see distinctly with both eyes ; 
and that it will .be very difficult, unless the two 
eyes differ so little in their direction, that the 
same object may be seen with both at the same 
time. Such patients I apprehend are rare; at 
least there are very few of them with whom I 
have had the fortune to meet : and therefore, for 
the assistance of those who may have happier op- 
portunities, and inclination to make the proper 
use of them, we shall consider the case of squint- 
ing hypothetically, pointing out the proper ar- 
ticles of inquiry, the observations that are want- 
ed, and the conclusions that may be drawn from 
them. 

1. It ought to be inquired, Whether the squint- 
ing person sees equally well with both eyes ? and 5 
if there be a defect in one, the nature and degree 
of that defect ought to be remarked. The ex- 
periments by which this may be done, are so ob- 
vious, that I need not mention them. But I 
would advise the observer to make the proper ex- 
periments, and not to rely upon the testimony of 



&58 OF THE HUMAN MIND. [CHAP. G. 

the patient; because I have found many instances, 
both of persons that squinted, and others, who 
were found, upon trial, to have a great defect in 
the sight of one eye, although they were never 
aware of it before. In all the following articles, 
it is supposed that the patient sees with both eyes 
so well, as to be able to read with either, when 
the other is covered. 

2. It ought to be inquired, Whether, when one 
eye is covered, the other is turned directly to the 
object? This ought to be tried in both eyes suc- 
cessively. By this observation, as a touch-stone 
we may try the hypothesis concerning squinting, 
invented by M. de la Hike, and adopted by Boer- 
haave, and many others of the medical faculty. 
The hypothesis is, That in one eye of a squint- 
ing person, the greatest sensibility and the most 
distinct vision is not, as in other men, in the 
centre of the retina, but upon one side of the 
centre ; and that he turns the axis of this eye 
aside from the object, in order that the picture 
of the object may fall upon the most sensible part 
of the retina, and thereby give the most distinct 
vision. If this is the cause of squinting, the 
squinting eye will be turned aside from the object, 
when the other eye is covered, as v/ell as when it 
is not. 

A trial so easy to be made, never was made for 
more than forty years ; but the hypothesis was 
very generally received. So prone are men to 
invent hypotheses, and so backward to examine 
them by facts. At last Dr. Jurin having made 



SECT. 15.] OF SEEING. 259 

the trial, found that persons who squint, turn the 
axis of the squinting eye directly to the object, 
when the other eye is covered. This fact is con- 
firmed by Dr. Porterfield ; and I have found 
it verified in all the instances that have fallen un- 
der my observation. 

3. It ought to be inquired, Whether the axes 
of the two eyes follow one another, so as to have 
always the same inclination, or make the same 
angle, when the person looks to the right or to 
the left, upward or downward, or straight for- 
ward. By this observation we may judge, whe- 
ther a squint is owing to any defect in the muscles 
which move the eye, as some have supposed. la 
the following articles we suppose that the inclin- 
ation of the axes of the eyes is found to be always 
the same. 

4. It ought to be inquired, Whether the per- 
son that squints sees an object single or double ? 

If he sees the object double; and if the two 
appearances have an angular distance equal to 
the angle which the axes of his eyes make with 
each other, it may be concluded that he hath 
corresponding points in the retince of his eyes, 
and that they have the same situation as in those 
who have no squint. If the two appearances 
should have an angular distance which is always 
the same, but manifestly greater or less than the 
angle contained under the optic axes, this would 
indicate corresponding points in the retina?, whose 
situation is not the same as in those who have no 

r 2 



260 OF THE HUMAN MIND. [CHAP. 6, 

squint; but it is difficult to judge accurately of 
the angle which the optic axes make. 

A squint too small to be perceived may occasion 
double vision of objects: for if we speak strictly, 
every person squints more or less, whose optic 
axes do not meet exactly in the object which he 
looks at. Thus, if a man can only bring the axes 
of his eyes to be parallel, but cannot make them 
converge in the least, he must have a small squint 
in looking at near objects, and will see them 
double, while he sees very distant objects single. 
Again, if the optic axes always converge, so as to 
meet eight or ten feet before the face at farthest, 
such a person will see near objects single ; but 
when he looks at very distant objects, he will 
squint a little and see them double. 

An instance of this kind is related by Aguilo* 
nitjs in his Optics ; who says, that he had seen a 
young man to whom near objects appeared single, 
but distant objects appeared double. 

Dr. Briggs, in his Nova visionis theoria, having 
collected from authors several instances of double 
vision, quotes this from Aguilonius, as the most 
wonderful and unaccountable of all, in so much 
that he suspects some imposition on the part of 
the young man : but to those who understand the 
laws by which single and double vision are re- 
gulated, it appears to be the natural effect of a 
very small squint* 

Double vision may always be owing to a small 
squint, when the two appearances are seen at a 



SECT. 15.] OF SEEING. ' 26l 

small angular distance, although no squint was 
observed : and I do not remember any instances 
of double vision recorded by authors, wherein 
any account is given of the angular distance of 
the appearances. 

In almost all the instances of double vision, 
there is reason to suspect a squint or distortion of 
the eyes, from the concomitant circumstances, 
which we find to be one or other of the following: 
the approach of death, or of a deliqaium, exces- 
sive drinking, or other intemperance, violent 
headach, blistering the head, smoking tobacco, 
blows or wounds in the head. In all these cases 
it is reasonable to suspect a distortion of the eyes, 
either from spasm, or paralysis in the muscles 
that move them. But although it be probable 
there is always a squint greater or less where 
there is double vision ; yet it is certain that there 
is not double vision always where there is a 
squint. I know no instance of double vision that 
continued for life, or even for a great number of 
years. We shall thererefore suppose in the follow- 
ing articles, that the squinting person sees objects 
single. 

5. The next inquiry then ought to be, Whe- 
ther the object is seen with both eyes at the same 
time, or only with the eye whose axis is directed 
to it? It hath been taken for granted, by the 
writers upon the strabismus, before Dr. Jurin, 
that those who squint commonly see objects 
single with both eyes at the same time ; but I 
know not one fact advanced bv any writer which 

.b3 



%6& OF THE HUMAN MIND. [CHAP. 6. 

proves it. Dr. Jurin is of a contrary opinion ; 
and as it is of consequence, so it is very easy to 
determine this point in particular instances, by 
this obvious experiment. While the person that 
squints looks steadily at an object, let the ob- 
serverj carefully remark the direction of both his 
eyes, and observe their motions ; and let an 
opaque body be interposed between the object 
and the two eyes successively. If the patient, 
notwithstanding this interposition, and without 
changing the direction of the eyes, continues to 
see the object all the time, it may be concluded 
that he saw it with both eyes at once. But if the 
interposition of the body between one eye and 
the object makes it disappear, then we may be 
certain, that it was seen by that eye only. In the 
two following articles, we shall suppose the first 
to happen, according to the common hypothesis. 

6. Upon this supposition, it ought to be in- 
quired, Whether the patient sees an object double 
in those circumstances wherein it appears double 
to them who have no squint? Let him, for in- 
stance, place a candle at the distance often feet, 
and holding his finger at arm's length between 
him and the candle, let him observe, when he looks 
•at the candle, whether he sees his finger with both 
eyes, and whether he sees it single or double; and 
when he looks at his finger, let him observe whe- 
ther he sees the candle with both eyes, and whe- 
ther single or double. 

By this observation, it may be determined, 
whether to this patient, the phenomena of double 



SECT. 15.] OF SEEING. 263 

as well as of single vision are the same as to them 
who have no squint. If they are not the same ; 
if he sees objects single with two eyes not only 
in the cases wherein they appear single, but in 
those also wherein they appear double to other 
men ; the conclusion to be drawn from this sup- 
position is, that his single vision does not arise 
from corresponding points in the retince of his 
eyes ; and that the laws of vision are not the same 
in him as in the rest of mankind. 

7- If, on the other hand, he sees objects double 
In those cases wherein they appear double to 
others, the conclusion must be, that he hath cor- 
responding points in the retince of his eyes, but 
unnaturally situate ; and their situation may be 
thus determined. 

When he looks at an object, having the axis 
of one eye directed to it, and the axis of the other 
turned aside from it ; let us suppose a right line 
to pass from the object through the centre of the 
diverging eye. We shall, for the sake of perspi- 
cuity, call this right line the natural axis oj the eyei 
and it will make an angle with i the real axis 
greater or less, according as his squint is greater 
or less. We shall also call that point of the retina 
in which the natural axis cuts it, the natural centre 
of the retina ; which will be more or less distant 
from the real centre, according as the squint is 
greater or less. 

Having premised these definitions, it will be 
evident to those who understand the principles 
of optics, that in this person the natural centre 



26& OF THE HUMAN MINI}. [CHAP. 6. 

of one retina corresponds with the real centre of 
the other, in the very same manner as the two 
real centres correspond in perfect eyes ; and that 
the points similarly situate with regard to the 
real centre in one retina, and the natural centre 
in the other, do likewise correspond, in the very 
same manner as the points similarly situate with 
regard to the two real centres correspond in per- 
fect eyes. 

If it is true, as has been commonly affirmed, 
that one who squints sees an object with both 
eyes at the same time, and yet sees it single, the 
squint will most probably be such as we have 
described in this article. And we may further 
conclude, that if a person affected with such a 
squint as we have supposed, could be brought to 
the habit of looking straight, his sight would 
thereby be greatly hurt. For he would then see 
every thing double which he saw with both eyes 
at the same time; and objects distant from one 
another, would appear to be confounded together. 
His eyes are made for squinting, as much as those 
of other men are made for looking straight ; and 
his sight would be no less injured by looking 
straight, than that of another man by squinting. 
He can never see perfectly, when he does not 
squint, unless the corresponding points of his eyes 
should by custom change their place ; but how 
small the probability of this is, will appear in the 
17th section. 

Those of the medical faculty who attempt the 
cure of a squint, would do well to consider whe- 



SECT. 15.] OF SEEING. 265 

ther it is attended with such symptoms as are 
above described. If it is, the cure would be 
worse than the malady : for every one will rea- 
dily acknowledge, that it is better to put up with 
the deformity of a squint, than to purchase the 
cure by the loss of perfect and distinct vision. 

8. We shall now return to Dr. Jurin's hypo- 
thesis, and suppose, that our patient when he saw 
objects single notwithstanding his squint, was 
found, upon trial, to have seen them only with 
one eye. 

We would advise such a patient, to endeavour 
by repeated efforts, to lessen his squint, and to 
bring the axes of his eyes nearer to a parallel di- 
rection. We have naturally the power of making 
small variations in the inclination of the optic 
axes ; and this power may be greatly increased by 
exercise. 

In the ordinary and natural use of our eyes, 
we can direct their axes to a fixed star \ in this 
case they must be parallel : we can direct them 
also to an object six inches distant from the eye ; 
and in this case the axis must make an angle of 
fifteen or twenty degrees. We see young people 
in their frolics learn to squint, making their eyes 
either converge or diverge, when they will, to a 
very considerable degree. Why should it be 
more difficult for a squinting person to learn to 
look straight when he pleases. If once, by an 
effort of his will, he can but lessen his squint, 
frequent practice will make it easy to lessen it, 
and will daily increase his power. So that if he 



266 OF THE HUMAN MIND. [CHAP. 6. 

begins this practice in youth, and perseveres in it, 
he may probably, after some time, learn to direct 
both his eyes to one object. 

When he hath acquired this power, it will be no 
difficult matter to determine, by proper observa- 
tions, whether the centres of the retina?, and other 
points similarly situate with regard to the centres, 
correspond, as in other men. 

9. Let us now suppose that he finds this to be 
the case ; and that he sees an object single with 
both eyes, when the axes of both are directed to 
it. It will then concern him to acquire the habit 
of looking straight, as he hath got the power, be- 
cause he will thereby not only remove a defor- 
mity, but improve his sight : and I conceive this 
habit, like all others, may be got by frequent ex- 
ercise. He may practise before a mirror when 
alone, and in company he ought to have those 
about him, who will observe and admonish him 
when he squints. 

10. What is supposed in the 9th article, is not 
merely imaginary ; it is really the case of some 
squinting persons, as will appear in the next sec- 
tion. Therefore it ought further to be inquired, 
How comes it to pass, that such a person sees an 
object which he looks at, only with one eye, when 
both are open ? In order to answer this question, 
it may be observed, first, Whether, when he 
looks at an object, the diverging eye is not drawn 
so close to the nose, that it can have no distinct 
images? Or, secondly, Whether the pupil of 
the diverging eye is not covered wholly, or in 



SECT. 15.] OF SEEING. 267 

part, by the upper eyelid ? Dr. Jurin observed 
instances of these cases in persons that squinted, 
and assigns them as causes of their seeing the 
object only with one eye. Thirdly, it may be 
observed, Whether the diverging eye is not so 
directed, that the picture of the object falls upon 
that part of the retina where the optic nerve en- 
ters, and where there is no vision ? This will 
probably happen in a squint wherein the axes of 
the eyes converge, so as to meet about six inches 
before the nose. 

11. In the last place, it ought to be inquired, 
"Whether such a person hath any distinct vision 
at all with the diverging eye, at the time he is 
looking at an object with the other? 

It may seem very improbable, that he should 
be able to read with the diverging eye when the 
other is covered, and yet, when both are open, 
have no distinct vision with it at all. But this 
perhaps will not appear so improbable, if the fol- 
lowing considerations are duly attended to. 

Let us suppose that one who saw perfectly, 
gets, by a blow on the head, or some other acci- 
dent, a permanent and involuntary squint. Ac- 
cording to the laws of vision, he will see objects 
double, and will see objects distant from one an- 
other confounded together : but such vision being 
very disagreeable, as well as inconvenient, he will 
do every thing in his power to remedy it. For 
alleviating such distresses, naVure often teaches 
men wonderful experiments, which the sagacity 
of a philosopher would be unable to discover. 



268 OF THE HUMAN MIND, [CHAP 6. 

Every accidental motion, every direction or con- 
formation of his eyes, which lessens the evil, will 
be agreeable ; it will be repeated, until it be learn- 
ed to perfection, and become habitual, even with- 
out thought or design. Now, in this case, what 
disturbs the sight of one eye, is the sight of the 
other ; and all the disagreeable appearances in 
vision would cease, if the light of one^eye was ex- 
tinct: The sight of one eye will become more dis- 
tinct and more agreeable, in the same proportion 
as that of the other becomes faint and indistinct. 
It may therefore be expected, that every habit 
will, by degrees, be acquired, which tends to 
destroy distinct vision in one eye, while it is pre- 
served in the other. These habits will be great- 
ly facilitated, if one eye was at first better than 
the other ; for in that case, the best eye will always 
be directed to the object which he intends to look 
at, and every habit will be acquired which tends 
to hinder his seeing at all, or seeing it distinctly 
by the other at the same time. 

I shall mention one or two habits that may 
probably be acquired in such a case; perhaps 
there are others which we cannot so easily conjecv 
ture. First, Bv a small increase or diminution 
of his squint, he may bring it to correspond with 
one or other of the cases mentioned in the last 
article. Secondly, The diverging eye may be 
brought to such a conformation as to be extreme- 
ly short sighted, rnd consequently to have no 
distinct vision of objects at a distance. I knew 
this to be the case of one person that squinted j 



SECT. 15.] OF SEEfNG. 269 

but cannot say whether the short-sightedness of 
the diverging eye was original or acquired by ha- 
bit. 

We see therefore, that one who squints, and 
originally saw objects double by reason of that 
squint, may acquire such habits, that when he 
looks at an object, he shall see it only with one 
eye : nay, he may acquire such habits, that when 
he looks at an object with his best eye, he shall 
have no distinct vision with the other at all. Whe- 
ther this is really the case, being unable to deter- 
mine in the instances that have fallen under my 
observation, I shall leave to future inquiry. 

I have endeavoured, in the foregoing articles, 
to delineate such a process as is proper in observ- 
ing the phenomena of squinting. I know well by 
experience, that this process appears more easy 
in theory than it will be found to be in practice ; 
and that in order to carry it on with success, 
some qualifications of mind are necessary in the 
patient, which are not always to be met with. — • 
But if those who have proper opportunities, and 
inclination to observe such phenomena, attend 
duly to this process, they may be able to furnish 
facts less vague and uninstructive than those we 
meet with, even in authors of reputation. By 
such facts vain theories may be exploded, and 
our knowledge of the laws of nature which regard 
the noblest of our senses, enlarged, 



270 OF THE HUMAN MIND. [CHAP 6. 

SECT. XVI. 

Facts relating to squinting. 

Having considered the phenomena of squinting 
hypothetically, and their connection with corres- 
ponding points in the relince, I shall now mention 
the facts I have had occasion to observe myself, 
or have met with in authors, that can give any 
light to this subject. 

Having examined above twenty persons that 
squinted, I found in all of them a defect in the 
sight of one eye. Four only had so much of dis- 
tinct vision in the weak eye, as to be able to read 
with it when the other was covered. The rest 
saw nothing at all distinctly with one eye. 

Dr . Porterfield says, that this is generally 
the case of people that squint : and I suspect it 
is so more generally than is commonly imagined. 
Dr. Jurin, in a very judicious dissertation upon 
squinting, printed in Dr. Smith's Optics, ob- 
serves that those who squint, and see objects with 
both eyes, never see the same object with both at 
the same time ; that when one eye is directed 
straight forward to an object, the other is drawn 
so close to the nose, that the object cannot at all 
be seen by it, the images being too oblique and 
too indistinct to affect the eye. In some squinting 
persons he observed the diverging eye drawn un- 
der the upper eyelid, while the other was directed 



SECT. 16.] OF SEEING. 2?1 

to the object. From these observations he con- 
cludes, " that the eye is thus distorted, not for the 
" sake of seeing better with it, but rather to avoid 
11 seeing at all with it as much as possible." From 
all the observations he had made, he was satisfied, 
that there is nothing peculiar in the structure of a 
Squinting eye; that the fault is only in its wrong 
direction ; and that this wrong direction is got 
by habit. Therefore he proposes that method of 
cure which we have described in the 8th and 9th 
articles of the last section. He tells us, that he 
had attempted a cure after this method, upon a 
young gentleman, with promising hopes of success; 
but was interrupted by his falling ill of the small- 
pox, of which he died. 

It were to be wished that Dr. Jurin had ac- 
quainted us whether he ever brought the young 
man to direct the axes of both eyes to the 
same object, and whether, in that case, he saw 
the object single, and saw it with both eyes ; 
and that he had likewise acquainted us, whether 
he saw objects double when his squint was di- 
minished. But as to these facts he is silent. 

I wished long for an opportunity of trying Dr. 
.Turin's method of curing a squint, without find- 
ing one; having always upon examination, dis- 
covered so great a defect in the sight of one eye 
of the patient as discouraged the attempt. 

But I have already found three young gentle* 
men, with whom I am hopeful this method may 
have success, if they have patience and persever- 
ance in using it. Two of them are brothers, and, 



272 OF THE HUMAN MIND. [CHAP. 6. 

before I had access to examine them, had been 
practising this method by the direction of their 
tutor, with such success, that the elder looks 
straight when he is upon his guard ; the younger 
can direct both his eyes to one objecj j but they 
soon return to their usual squint. 

A third young gentleman, who had never heard 
of this method before, by a few days practice was 
able to direct both his eyes to one object, but 
could not keep them long in that direction. All 
the three agree in this, that when both eyes are 
directed to one object, they see it and the adja- 
cent objects single ; but when they squint they 
see objects sometimes single and sometimes dou- 
ble. I observed of all the three, that when they 
squinted most, that is, in the way they had been 
accustomed to, the axes of their eyes converged, 
so as to meet five or six inches before the nose. — > 
It is probable that in this case the picture of the 
object in the diverging eye, must fall upon that 
part of the retina where the optic nerve enters ; 
and therefore the object could not be seen by that 
eye. 

All the three have some defect in the sight of 
one eye, which none of them knew until I put 
them upon making trials: and when they squint, 
the best eye is always directed to the object, and 
the weak eye is that which diverges from it.— «■ 
But when the best eye is covered, the weak eye 
is turned directly to the object. Whether this 
defect of sight in one eye, be the effect of its 
having been long disused, as it must have been 



SECT. 16.] OF SEEING. 273 

when they squinted ; or whether some original 
defect in one eye might be the occasion of their 
squinting, time may discover. The two brothers 
have found the sight of the weak eye improved 
by using to read with it while the other is cover- 
ed. The elder can read an ordinary print with 
the weak eye ; the other, as well as the third 
gentleman, can only read a large print with the 
weak eye. I have met with one other person 
only who squinted, and yet could read a large 
print with the weak eye. He is a young man, 
whose eyes are both tender and weak-sighted, 
but the left much weaker than the right. When 
he looks at any object, he always directs the right 
eye to it, and then the left is turned towards the 
nose so much, that it is impossible for him to see 
the same object with both eyes at the same time. 
When the right eye is covered, he turns the left 
directly to the object ; but he sees it indistinctly, 
and as if it had a mist about it. 

I made several experiments, some of them in 
the company, and with the assistance of an inge- 
nious physician, in order to discover, whether ob- 
jects that were in the axes of the two eyes, were 
seen in one place confounded together, as in 
those who have no involuntary squint. The ob- 
ject placed in the axis of the weak eye was a 
lighted candle at the distance of eight or ten 
feet. Before the other eye was placed a printed 
book, at such a distance as that he could read 
upon. He said, that while he read upon the 
book, he saw the candle but very faintly. 

s 



£7^ OF THE HUMAN MIND. CHAP. 6. 

from what we could learn, these two objects did 
not appear in one place, but had ail that angular 
distance in appearance which they had in reality. 

If this was really the case, the conclusion to be 
drawn from it is, that the corresponding points 
in his eyes, are not situate in the same manner as 
in other men ; and that if he could be brought 
to direct both eyes to one object, he would see it 
double. But considering that the young man 
had never been accustomed to observations of this 
kind, and that the sight of one eye was so im- 
perfect, I do not pretend to draw this conclusion 
with certainty from this single instance. 

All that can be inferred from these facts is, 
that of four persons who squint, three appear to 
have nothing preternatural in the structure of 
their eyes. The centres of the retina? t and the 
points similarly situate with regard to the centres, 
do certainly correspond in the same manner as 
in other men. So that if they can be brought to 
the habit of directing their eyes right to an ob- 
ject, they will not only remove a deformity, but 
improve their sight. With regard to the fourth, 
the case is dubious, with some probability of a 
deviation from the usual course of nature in the 
situation of the corresponding points of his eyes. 



SECT. 17.] OF SEEING. 2?'5 

SECT. XVII. 

Of the effect of custom in seeing objects single. 

It appears from the phenomena of single and 
double vision recited in Sect. 13. that our see- 
ing an object single with two eyes, depends up- 
on these two things. First, Upon that mutual 
correspondence of certain points of the retinae 
which we have often described. Secondly, Up- 
on the two eyes being directed to the object so 
accurately, that the two images of it fall upon 
corresponding points. These two things must 
concur in order to our seeing an object single 
with two eyes ; and as far as they depend upon 
custom, so far only can single vision depend upon 
custom. 

With regard to the second, that is, the accu- 
rate direction of both eyes to the object, I think, 
it must be acknowledged that this is only learned 
by custom. Nature hath wisely ordained the 
eyes to move in such a manner, that their axes 
shall always be nearly parallel \ but hath left it in 
our power to vary their inclination a little ac- 
cording to the distance of the object we look at. 
Without this power, objects would appear single 
at one particular distance only ; and, at distances 
much less, or much greater, would always appear 
double. The wisdom of nature is conspicuous in 
giving us this power, and no less conspicuous in 



%J6 OF THE HUMAN MIND. [CHAP. 6. 

making the extent of it exactly adequate to the 
end. 

The parallelism of the eyes, in general,' is there- 
fore the work of nature ; but that precise and ac- 
curate direction, which must be varied according 
to the distance of the object, is the effect of cus- 
tom. The power which nature hath left us of 
varying the inclination of the optic axes a little, 
Is turned into a habit of givng them always that 
inclination which is adapted to the distance of 
the object. 

But it may be asked, What gives rise to this 
habit? The only answer that can be given to this 
question is, that it is found, necessary to perfect 
and distinct vision. A man who hath lost the 
sight of one eye, very often loses the habit of 
directing it exactly to the object he looks at, be- 
cause that habit is no longer of use to him. And 
if he should recover the sight of his eye, he would 
recover this habit, by finding it useful. No part 
of the human constitution is more admirable than 
that whereby we acquire habits which are found 
useful, without any design or intention. Chil- 
dren must see imperfectly at first ; but by using 
their eyes they learn to use them in the best 
manner, and acquire, without intending it, the 
habits necessary for that purpose. Every man 
becomes most expert in that kind of vision which 
is most useful to him in his particular profession 
and manner of life. A miniature painter, or an 
engraver, sees very near objects better than a 
sailor j but the sailor sees very distant objects much 



SECT. 17.] OF SEEING. Tfl 

better than they. A person that is shortsighted, 
in looking at distant objects, gets the habit of 
contracting the aperture of his eyes, by almost 
closing his eye-lids. Why ? For no other rea- 
son, but because this makes him see the object 
more distinct. In like manner, the reason why 
every man acquires the habit of directing both 
eyes accurately to the object, must be, because 
thereby he sees it more perfectly and distinctly. 

It remains to be considered, whether that cor- 
respondence between certain points of the retina?, 
which is likewise necessary to single vision, be 
the effect of custom, or an original property of 
human eyes. 

A strong argument for its being an original 
property, may be drawn from the habit just now 
mentioned, of directing the eyes accurately to an 
object. This habit is got by our finding it neces- 
sary to perfect and distinct vision. But why is 
it necessary? For no other reason but this, be- 
cause thereby the two images of the object falling 
upon corresponding points, the eyes assist each 
other in vision, and the object is seen better by 
both together, than it could be by one ; but when 
the eyes are not accurately directed, the two 
images of an object fall upon points that do not 
correspond, whereby the sight of one eye disturbs 
the sight of the other, and the object is seen more 
indistinctly with both eyes than it would be with 
one. Whence it is reasonable to conclude, that 
this correspondence of certain points of the rc- 
tince, is prior to the habits we acquire in virion, 



278 OF THE HUMAN MIND. CHAP. 6. 

and consequently is natural and original. We 
have all acquired the habit of directing our eyes 
always in a particular manner, which causes single 
vision. Now, if nature hath ordained that we 
should have single vision only, when our eyes are 
thus directed, there is an obvious reason why all 
mankind should agree in the habit of directing 
them in this manner. But if single vision is the 
effect of custom, any other habit of directing the 
eyes would have answered the purpose ; and no 
account can be given why this particular habit 
should be so universal; and it must appear very 
strange, that no one instance hath been found of 
a person who had acquired the habit of seeing 
objects single with both eyes, while they were di- 
rected in any other manner. 

The judicious Dr. Smith, in his excellent Sys- 
tem of Optics, maintains the contrary opinion, 
and oners some reasonings and facts in proof of 
it. He agrees with Bishop Berkeley in attri- 
buting it entirely to custom, that we see objects 
single with two eyes, as well as that we see ob- 
jects erect by inverted images. Having consi- 
dered Bishop Berkeley's reasonings in the 11th 
section, we shall now beg leave to make some re- 
marks on what Dr. Smith hath said upon this 
subject, with the respect due to an author to 
whom the world owes, not only many valuable 
discoveries of his own, but those of the brightest 
mathematical genius of this age, which, with 
great labour, he generously redeemed from obli- 
vion. 



SECT, 17.] OF SEEING. . 279 

He observes, that the question, Why we see 
objects single with two eyes ? is of the same sort 
with this, why we hear sounds single with two 
ears ; and that the same answer must serve both. 
Tiie inference intended to be drawn from this 
observation is, that as the second of these pheno- 
mena is the effect of custom, so likewise is the 
first. 

Now, I humbly conceive that the questions 
are not so much of the same sort, that the same 
answer may serve for both ; and moreover, thai 
our hearing single with two ears is not the effect 
of custom. 

Two or more visible objects, although perfectly 
similar, and seen at the very same time, may be 
distinguished by their visible places ; but two 
sounds perfectly similar, and heard at the same 
time, cannot be distinguished ; for, from the na- 
ture of sound, the sensations they occasion must 
coalesce into one. and lose ail distinction. If 
therefore it is asked, Whv we hear sounds single 
with two ears? I answer, Not from custom ; but 
because two sounds which are perfectly like and 
synchronous, have nothing by which they can be 
distinguished. But will this answer fit the other 
question ? I think not. 

The object makes an appearance to each eye, 
as the sound makes an impression upon each ear; 
so far the two senses Agree. But the visible ap- 
pearances may be distinguished ; by place, when 
perfectly like in other respects ; the sounds can- 
not be thus distinguished j and herein the two 



£80 OF THE HUMAN MIND. CHAP. 6. 

senses differ. Indeed, if the two appearances 
have the same visible place, they are, in that 
case, as incapable of distinction as the sounds 
were, and we see the object single. But when 
they have not the same visible place, they are 
perfectly distinguishable, and we see the object 
double. We see the object single only, when the 
eyes are directed in one particular manner, while 
there are many other ways of directing them 
within the sphere of our power, by which we see 
the object double. 

Dr. Smith justly attributes to custom that well-? 
known fallacy in feeling, whereby a button pressed 
with two opposite sides of two contiguous fingers 
laid across is felt double. I agree with him, 
that the cause of this appearance is, that those 
opposite sides of the fingers have never been 
used to feel the same object, but two different ob- 
jects, at the same time. And I beg leave to add, 
that as custom produces this phenomenon, so a 
contrary custom destroys it: for if a man fre- 
quently accustoms himself to feel the button with 
his ringers across, it will at last be felt single ; as 
I have found by experience. 

It may be taken for a general rule, That things 
which are produced by custom, may be undone 
or changed by disuse, or by contrary custom. 
On the other hand, it is a strong argument, that 
an effect is not owing to custom, but to the con- 
stitution of nature, when a contrary custom, long 
continued, is found neither to change nor weaken 
it. I take this to be the best rule by which we 



SECT. 17.] OF SEEING. 281 

can determine the question presently under con- 
sideration. I shall therefore mention two facts 
brought by Dr. Smith to prove that the corre- 
sponding points of the retina? have been changed 
by custom ; and here I shall mention some facts 
tending to prove, that there are corresponding 
points of the retinas of the eyes originally, and that 
custom produces no change in them. 

" One fact is related upon the authority of 
" Martin Folxes, Esq. who was informed by 
" Dr. Hepburn of Lynn, that the Reverend Mr. 
^ Foster of Clinchwarton, in that neigbbour- 
" hood, having been blind for some years of a 
" gutta serena, was restored to sight by salivation : 
" and that upon his first beginning to see, ail ob- 
jects appeared to him double; but afterwards 
" the two appearances approaching by degrees, 
" he came at last to see single, and as distinctly 
*' as he did before he was blind. " 

Upon this case I observe, first, That it does 
not prove any change of the corresponding points 
of the eyes, unless we suppose what is not affirm- 
ed, that Mr. Foster directed his eyes to die ob- 
ject at first, when he saw double, with the same 
accuracy, and in the same manner, that he did 
afterwards when he saw single. Secondly, If we 
should suppose this, no account can be given, 
why at first the two appearances should be seen at 
one certain angular distance rather than another; 
or why this angular distance should gradually de- 
crease, until at last the appearances coincided. 
How could thiseftect be produced by custom? But, 



2S2 OF THE HUMAN MIND. [CHAP 6. 

thirdly, Every circumstance of this case may be 
accounted for, on the supposition that Mr. Foster 
had corresponding points on the retina? of his eyes 
from the time he began to see, and that custom- 
made no change with regard to them. We need" 
only further suppose, what is common in such' 
cases, that by some years blindness he had lost the 
habit of directing his eyes accurately to an object, 
and that he gradually recovered this habit wh-en. 
he came to see. 

The second fact mentioned by Dr. Smith is 
taken from Mr. Cheselden's Anatomy ; and is 
this: "A gentleman who, from a blow on the 
" head, had one eye distorted* found every object 
" appear double ; but by degrees the most fami- 
* ! liar ones became single ; and in time ail objects 
" became so, without any amendment of the dis- 
^ tortion." 

I observe here, that it is not said that the two 
appearances gradually approached, and at last 
united, without any amendment of the distortion. 
This would indeed have been a decisive proof of 
a change in the corresponding points of the re- 
tina? > and yet of such a change as could not be 
accounted for from custom. But this is not said ; 
and if it had been observed, a circumstance so 
remarkable would have been mentioned by Mr. 
Cheselden, as it was in the other case by Di\ 
Hepburn. We may therefore take it for grant- 
ed, that one of the appearances vanished by de- 
grees, without approaching to the other. And 
this I conceive might haopen several ways. First* 



SECT. 17.] OF SEEING. 283 

The sight of the distorted eye might gradually 
decay by the hurt ; so the appearances presented 
by that eye would gradually vanish. Secondly, 
A small and unperceived change in the manner 
of directing the eyes, might occasion his not see- 
ing the object with the distorted eye, as appears 
from Sect. 15. Art. 10. Thirdly, By acquiring the 
habit of directing one and. the same eye always to 
the object, the faint and oblique appearance, pre- 
sented by the other eye, might be so little attended 
to when it became familiar, as not to be perceived. 
One of these causes, or more of them concur- 
ring, might produce the effect mentioned, with- 
out any change of the corresponding points of the 
eyes. 

For these reasons, the facts mentioned by Dr. 
Smith, although curious, seem not to be decisive. 

The following facts ought to be put in the op- 
posite scale. First, In the famous case of the 
young gentleman couched by Mr. Cheselden - , 
after having had cataracts on both eyes until lie 
was thirteen years of age, it appears that he saw 
objects single from the time he began to see with 
both eyes. Mr. Cheselden's words are: " And 
" now being lately couched of his ether eye, he 
<c says, that objects at first appeared large to this 
" eye, but not so large as they did at first to the 
" other ; and looking upon the same object with 
" both eyes, he thought it looked about twice as 
" large as with the first couched eye only, but not 
" double, that we can anywise discover/' 

Secondly, The three young gentlemen men- 



%S4t OF THE HUMAN MIND. [CHAP. 6. 

tioned in the last section, who had squinted, as 
far as I know from infancy ; as they learned to 
direct both eyes to an object, saw it single. In 
these four cases, it appears evident, that the cen- 
tres of the rct'inm corresponded originally, and 
before custom could produce any such effect : 
for Mr, Cheselden's young gentleman had ne- 
ver been accustomed to see at all before he was 
couched ; and the other three had never been 
accustomed to direct the axes of both eyes to the 
object. 

Thirdly, From the facts recited in Sect. 13. it 
appears, That from the time we are capable of 
observing the phenomena of single and double 
vision, custom makes no change in them. 

I have amused myself with such observations 
for more than thirty years ; and in every case 
wherein I saw the object double at first, I see it so 
to this day, notwithstanding the constant experi- 
ence of its bemg single. In other cases where 1 
know there are two objects, there appears only 
one, after thousands of experiments. 

Let a man look at a familiar object through a 
polyhedron or multiplying glass every hour of 
Ins life, the number of visible appearances will 
be the same at last as at first : nor does any num- 
ber of experiments, • or length of time, make the 
least change. 

Effects produced by habit, must vsry accord- 
ing as the acts by which the habit is acquired are 
more or less frequent: but the phenomena of 
single and double vision are so invariable and 



SECT. IS.] OF SEEING. %S5 

uniform in all men, are so exactly regulated by 
mathematical rules, that I think we have good 
reason to conclude, that they are not the effect 
of custom, but of fixed and immutable laws of 
nature. 



SECT. XVIII. 



Of Dr. Porterfield's account of single and double 

vision. 

Bishop Berkeley and Dr. S:.iixn seem to attri- 
bute too much to custom in vision ; Dr. Porter- 
field too little. 

This ingenious writer thinks, that by an origi- 
nal law of our nature, antecedent to custom and 
experience, we perceive visible objects in their 
true place, not only as to their direction, but like- 
wise as to their distance from the eye : and there- 
fore he accounts for our seeing objects single, 
with two eyes, in this manner. Having the fa- 
culty of perceiving the object with each eye 
in its true place, we must perceive it with' both 
eyes in the same place; and consequently must 
perceive it single. 

He is aware, that this principle, although it 
accounts for our seeing objects single with two 
eyes, yet does not at all account for our seeing 
objects double ; and whereas other writers on this 
subject take it to be a sufficient cause for double 
vision that we have two eyes, and only find it 



286 OF THE HUMAN MIND. [CHAP. 6. 

difficult ' to assign a cause for single vision ; on 
the contrary Dr. Forterfield's principle throws 
all the difficulty on the other side. 

Therefore, in order to account for the- pheno- 
mena of double vision he advances another prin- 
ciple, without signifying whether he conceives 
it to be an original law of our nature, or the effect 
of custom. It is, That our natural perception of 
the distance of objects from the eye, is not ex- 
tended to all the objects that fall within the field 
of vision, but- limited to that which we directly 
look at ; and that the circumjacent objects, what- 
ever be their real distance, • are seen at the same 
distance with the object we look at ; as if they 
were all in the surface of a sphere whereof the 
eye is the centre. 

Thus, single vision is accounted for by our 
seeing the true distance of an object which we 
look at; and double vision, by a false appearance 
of distance in objects which we do not directly 
look at. 

We agree with this learned and ingenious au- 
thor, that it is by a natural and original principle 
that we see visible objects in a certain direction 
from the eye, and honour him as the author of 
this discovery : but we cannot assent to either of 
those principles by which he explains single and 
double vision, for the following reasons : 

1. Our having a natural and original percep- 
tion of the distance of objects from the eye, ap- 
pears contrary to a well attested fact : for the 
young gentleman couched by Mr. Cheselden 



SECT. 18.] OF SEEING. 28? 

imagined, at first, that whatever he saw touched 
his eye, as what he felt touched his hand. 

2. The perception we have of the distance of 
objects from the eye, whether it be from nature 
or custom, is not so accurate and determi- 
nate as is necessary to produce single vision. — 
A mistake of the twentieth or thirtieth part of 
the distance of a small object, such as a pin, 
ought, according to Dr. Porterfield's hypo- 
thesis, to make it appear double. Very few can 
judge of the distance of a visible object with such 
accuracy. Yet we never find double vision pro- 
duced by mistaking the distance of the object.— 
There are many cases in vision, even with the 
naked eye, wherein we mistake the distance of 
an object by one half or more : why do we see 
such objects single? When I move my spectacles 
from my eyes towards a small object, two or three 
feet distant, the object seems to approach, so as 
to be seen at last at about half its real distance ; 
but it is seen single at that apparent distance, as 
well as when we see it with the naked eye at its 
real distance. And when we look at an object 
with a binocular telescope, properly fitted to the 
eyes, we see it single, while it appears fifteen or 
twenty times nearer than it is. There are then few- 
cases wherein the distance of an object from the 
eye is seen so accurately as is necessary for single 
vision, upon this hypothesis : This seems to be a 
conclusive argument against the account given of 
single vision. We find, likewise, that false judg- 
ments or fallacious appearances of the distance 



288 OF THE HUMAN MIND. [CHAP. 6. 

an object, do not produce double vision. This 
seems to be a conclusive argument against the 
account given of double vision. 

3. The perception we have of the linear dis- 
tance of objects, seems to be wholly the effect of 
experience. This I think hath been proved by 
Bishop Berkeley and by. Dr. Smith ; and when 
we come to point out the means of judging of 
distance by sight, it will appear that they are all 
furnished by experience. • 

4. Supposing that by a law of our nature, the 
distances of objecis from the eye were perceived 
most accurately, as well as their direction, it will 
not follow that we must see the object single. 
Let us consider what means such a law of nature 
would furnish for resolving the question, Whether 
the objects of the two eyes are in one and the 
same place, and consequently are not two, but 
one ? 

Suppose them two right lines, one drawn from 
the centre of one eye to its object, the other 
drawn, in like manner, from the centre of the 
other eye to its object. This law of nature gives 
us the direction or position of each of these right 
lines, and the length of each ; and this is all that 
it gives. These are geometrical data, and we 
may learn from geometry what is determined by 
their means. Is it then determined by these da- 
ta, Whether the two right lines terminate in one 
and the same point, or not? No truly. In order 
to determine this, we must have three other data. 
We must know whether the two right lines are 



SECT. 18.] OF SEEING. 289 

in one plane : we must know what angle they 
make, and we must know the distance between 
the centres of the eyes. And, when these things 
are known, we must apply the rules of trigono- 
metry, before we can resolve the question, Whe- 
ther the objects of the two eyes- are in one and 
the same place ; and consequently whether they 
are two or one ? 

5. That false appearance of distance into which 
double vision is resolved, cannot be the effect of 
custom; for constant experience contradicts it: 
Neither hath it the features of a law of nature ; 
because it does not answer any good purpose, 
nor indeed any purpose at all but to deceive us. 
But why should we seek for arguments, in a ques- 
tion concerning what appears to us, or does not 
appear? The question is, At what distance do the 
objects now in my eye appear ? Do they all ap- 
pear at one distance, as if placed in the concave 
surface of a sphere, the eye being' in the centre? 
Every man surely may know this with certainty ; 
and, if he will but give attention to the testimony 
of his eyes, needs not ask a philosopher, how vi- 
sible objects appear to him. Now, it is very 
true, that if I look up to a star in the heavens, 
the Other stars that appear at the same time do 
appear in this manner : Yet this phenomenon 
does not favour Dr. Porterfield's hypothesis ; 
for the stars and heavenly bodies do not appear 
at their true distances when we look directly to 
them, any more than when they are seen oblique- 
ly, and if this phenomenon be an argument for 

T 



290 OF THE HUMAN MIND. CHAF. 6. 

Dr. PofvTErfield's second principle, it must de- 
stroy the first. 

The true cause of this phenomenon will be 
given afterwards ; therefore, setting it aside for 
the present, let us put another case. I sit in my 
room, and direct my e)-es to the door, which ap- 
pears to be about sixteen feet distant : at the 
same time I see many other objects faintly and 
obliquely ; the floor, floor-cloth, the table which 
I write upon, papers, standish, candle, &c. Now, 
do all these objects appear at the same distance 
of sixteen feet? Upon the closest attention, I find 
they do not. 



SECT. XIX, 



Of Dr. Brigg's theory, and Sir Issac Newton's 
conjecture on this sul/ject. 

I am afraid the reader, as well as the writer, is 
already tired of the subject of single and double 
vision. The multitude of theories advanced by 
authors of great name, and the multitude of facts 
observed without sufficient skill in optics, or relat- 
ed without attention to the most material and de- 
cisive circumstances, have equally contributed to 
perplex it. 

In order to bring it to some issue, T have, in 
the 13th section, given a more full and regular 
deduction than had been given heretofore, of the 
phenomena of single and double vision, in those 



SECT. 17.] OF SEEING. 291 

whose sight is perfect ; and have traced them up 
to one general principle, which appears to be a 
law of vision in human eyes that are perfect and 
in their natural state. 

In the 14th section I have made it appear, 
that this law of vision, although excellently adapt- 
ed to the fabric of the human eyes, cannot answer 
the purposes of vision in some other animals - y 
and therefore, very probably, is not common to 
all animals. The purpose of the loth and 16th 
sections is, to inquire, whether there be any de- 
viation from this law of vision in those who squint? 
a question which is of real importance in the me- 
dical art, as well as in the philosophy of vision ; 
but which after all that hath been observed and 
written on the subject, seems not to be ripe for 
a determination, for want of proper observations. 
Those who have had skill to make proper obser- 
vations, have wanted opportunities ; and those 
who have had opportunities, have wanted skill or 
attention. I have therefore thought it worth 
while to »give a distinct account of the observa- 
tions necessary for the determination of this ques- 
tion, and what conclusions may be drawn from 
the facts observed. I have likewise collected, 
and set in one view, the most conclusive facts 
that have occurred in authors, or have fallen under 
my own observation. 

It must be confessed, that these facts, when 
applied to the question in hand, make a very poor 
figure : and the gentlemen of the medical faculty 
are called upon, for the honour of their profes- 

T 2 



%9% OF THE HUMAN MIND. CHAP. 6. 

sion, and for the benefit of mankind, to add to 
them. 

All the medical, and all the optical writers, 
upon the strabismus, that I have met with, except 
Dr. Jurin, either affirm, or take it for granted, 
that squinting persons see the object with both 
eyes, and yet see it single. Dr. Jurin affirms, 
that squinting persons never see the object with 
both eyes ; and that if they did, they would see 
it double. If the common opinion, be true, the 
cure of a squint would be as pernicious to the 
sighj: of the patient, as the causing of a perma- 
nent squint would be to one who naturally had 
no squint : and therefore no physician ought to 
attempt such a cure ; no patient ought to submit 
to it. But if Dr. Jurin's opinion be true, most 
young people that squint may cure themselves, 
by taking some pains ; and may not only remove 
the deformity, but at the same time knprcv? their 
sight. If the common opinion be true, the centres 
and other points of the two retina; in squinting 
persons do not correspond as in other men, and 
nature in them deviates from her common rule. 
But if Dr. Jurin's opinion be true, there is reason 
to think that the same general laws of vision which 
we have found in perfect human eyes, extend also 
to those which squint. 

It is impossible to determine, by reasoning, 
which of these opinions is true ; or whether one 
may not be found true in some patients, and the 
other in others. Here experience and observation 
are our only guides ; and a deduction of instances 



SECT. 19.] OF SEEING. 293 

is the only rational argument. It might therefore 
have been expected, that the patrons of the con- 
trary opinions should have given instances in 
support of them that are clear and indisputable : 
but I have not found one such instance on either 
side of the question, in ail the authors I have 
met with. I have given three instances from my 
own observation, in confirmation of Dr. Jurin's 
opinion, which admit of no doubt; and one 
which leans rather to the other opinion, but is 
dubious. And here I must leave the matter to 
further observation. 

In the 17th section, I have endeavoured to 
shew, that the correspondence am*l sympathy of 
certain points of the two reli?iw 9 into which we 
have resolved all the phenomena of single and 
double vision, is not, as Dr. Smith conceived, 
the effect of custom, nor can be changed by cus- 
tom, but is a natural and original property of hu- 
man eyes: and in the last section, that it is not 
owing to an original and natural perception of 
the true distance of objects from the eye, as Dr. 
Porterfield imagined. After this recapitula- 
tion, which is intended to relieve the attention 
of the reader, shall we enter into more .theories 
upon this subject ? 

That of Dr. Briggs, first published in English, 
in the Philosophical Transactions, afterwards in 
Latin, under the title of N ova visionis theoria, with 
a prefatory epistle of Sir Isaac Newton to the 
author, amounts to this, That the fibres of the 
optic nerves passing from, corresponding points of 



29^ OF THE HUMAN MIND. [CHAP. 6. 

the retince to* the thatami nervorum opticorum, hav- 
ing the same length, the same tension, and a si- 
milar situation, will have the same tone ; and 
therefore their vibrations, excited by the impres- 
sion of the rays of light, will be like unisons in 
music, and will present one and the same image- 
to the mind : but the fibres passing from parts of 
the retince which do not correspond, having dif- 
ferent tensions and tones, will have discordant 
vibrations ; and therefore present different images 
to the mind. 

I shall not enter upon a particular examination 
of this theory. It is enough to observe in gene- 
ral, that it is a system of conjectures concerning 
things of which we are entirely ignorant ; and 
that all such theories in philosophy deserve rather 
to be laughed at, than to be seriously refuted. 

From the first dawn of philosophy to this day 
it hath been believed that the optic nerves are 
intended to carry the images of visible objects- 
from the bottom of the eye to the mind ; and that 
the nerves belonging to the organs of the other 
senses have a like office. But how do we know 
this? We conjecture it: and taking this conjec- 
ture for a truth, we consider'how the nerves may 
best answer this purpose. The system of the; 
nerves for many ages was taken to be a hydraulic 
engine, consisting of a bundle of pipes, which 
carry to and fro a liquor called animal spirits. 
About the time of Dr. Brigg's, it was thought 
rather to be a stringed instrument, composed of 
vibrating-chords, each of which had its proper 



SECT. 19.] OF SEEING. £95 

tension and tone. But some, with great proba- 
bility, conceived it to be a wind instrument, 
which played its part by the vibrations of an elas- 
tic ether in the nervous fibrils. 

These, I think, are all the engines into which 
the nervous system hath been moulded by philo- 
sophers, for conveying the images of sensible 
things from the organ to the sensorium. And for 
all that we know of the matter, every man may 
freely choose which he thinks fittest for the pur- 
pose ; for, from fact and experiment, no one of 
them can claim preference to another. Indeed, 
they all seem so unhandy engines for carrying 
images, that a man would be tempted to invent 
a new one. 

Since, therefore, a blind man may guess as well 
in the dark as one that sees, I beg leave to offer 
another conjecture touching the nervous system, 
which I hope will answer the purpose as well as 
those we have mentioned, and which recom- 
mends itself by its simplicity. Why may not the 
optic nerves, for instance, be made up of empty 
tubes, opening their mouths wide enough to re- 
ceive the rays of light which form the image up- 
on the retina.) and gently conveying them safe, 
and in their proper order, to the xtry seat of the 
soul, until they flash in her face ? It is easy for 
an ingenious philosopher to fit the calibre of these 
empty tubes to the diameter of the particles of 
light, so as they shall receive no grosser kind of 
matter. And if these rays should be in danger 
of mistaking their way, an expedient may also be 



295 OF THE HUMAN MIND. [CHAP.6. 

found to prevent this. For it requires no more 
than to bestow upon the tubes of the nervous 
system a peristaltic motion, like that of the ali- 
mentary tube. 

It is a peculiar advantage of this hypothesis, 
that although ail philosophers believe that the 
species or images of things are conveyed by the 
nerves to the soul, yet none of their hypotheses 
show how this may be done. For how can ima- 
ges of sound, taste, smell, colour, figure, and all 
sensible qualities, be made out of the vibrations 
of musical chords, or the undulations of animal 
spirits, or of ether? We ought not to suppose 
means inadequate to the end. Is it "not as philo- 
sophical, and more intelligible, to conceive, that 
as the stomach receives its food, so the soul re- 
ceives her images by a kind of nervous degluti- 
tion ? I might add, that we need only continue 
this peristaltic motion of the nervous tubes from 
the sensorium to the extremities of the nerves that 
serve the muscles, in order to account for muscu- 
lar motion. 

Thus nature will be consonant to herself; and 
as sensation will be the conveyance of the ideal 
aliment to the mind, so muscular motion will be 
the expulsion of the recrementitious part of it*. 
For who can deny, that the images of things con- 
veyed by sensation, may, after due concoction, 
become fit to be thrown off by muscular motion? 
I only give hints of these things to the ingenious, 
hoping that in time this hypothesis may be 
wrought up into a system as truly philosophical, 



SECT. 15. J OF SEEING. 29? 

as that of animal spirits, or the vibration of nerv- 
ous fibres. 

To be serious : In the operations of nature,' I 
hold the theories of a philosopher, which are un- 
supported by fact, in the same estimation with 
the dreams of a man asleep, or the ravings of a 
madman. We laugh at the Indian philosopher, 
who, to account for the support of the earth, con- 
trived. the hypothesis of a huge elephant, and to 
support the elephant a huge tortoise. If we will 
candidly confess the truth, we know as little of 
the operation of the nerves, as he did of the man- 
ner in which the earth is supported; and our hy- 
pothesis about animal spirits, or about the ten- 
sion and vibrations of the nerves are as like to 
be true, as his about the support of the earth. — 
His elephant was a hypothesis, and our hypothe- 
ses are elephants. Every theory in philosophy, 
which is built on pure conjecture, is an elephant; 
and every theory that is supported partly by fact, 
and partly by conjecture, is like Nebuchadnez- 
zar's image, whose feet was partly of' iron, and 
partly of clay. 

The great Newton first gave an example to 
philosophers, which always ought to be, but rare- 
ly hath been followed, by distinguishing his con- 
jectures from his conclusions, and putting the 
former by themselves, in the modest form of que- 
ries. This is fair and legal ; but all other philo- 
sophical traffic in conjecture, ought to be held 
contraband and illicit. Indeed his conjectures 
have commonly more foundation in fact, and 



298 OF THE HUMAN MIND. [CHAP. 6. 

more verisimilitude, than the dogmatical theories 
of most other philosophers ; and therefore we 
ought not to omit that which he hath offered 
concerning the cause of our seeing objects single 
with two eyes, in the 15th query annexed to his 
Optics* 

«' Are not the species of objects seen with both 
" eyes, united where the optic nerves meet, be- 
" fore they come into the brain, the fibres on the 
" right side of both nerves, uniting there, and 
" after union going thence into the brain in the 
" nerve which is on the right side of the head, 
« and the fibres on the left side of both nerves 
« 6 uniting in the same place, and after union go- 
" ing into the brain in the nerve which is on the 
<; left side of the head; and these two nerves 
" meeting in the brain in such a manner that 
" their fibres make but one entire species or pic- 
" ture, half of which on the right side of the 
" sensorium comes from the right side of both 
" eyes through the right side of both optic nerves, 
*' to the place where the nerves meet, and from 
" thence to the right side of the head into the 
§i brain, and the other half on the left side of the 
*« sensorium comes, in like manner, from the left 
•' side of both eyes ? For the optic nerves of such 
«' animals as look the same way with both eye?, 
*« (as men, dogs, sheep, oxen, &c.)> meet before 
" they come into the brain ; but the optic nerves 
" of such animals as do not look the same way 
" with both eyes, (as of fishes and of the cha- 
" melon.) do pot meet, if I am rightly infbrm- 
" ed." 



ECT. 19.] OF SEEING. 299 

1 beg leave to distinguish this query into two, 
which are of very different natures; one being 
purely anatomical, the other relating to the car- 
rying species or pictures of visible objects to the 
sensorium. 

The first question is, Whether the fibres com- 
ing from corresponding points of the two retina 7 , 
do not unite at the place where the optic nerves 
meet, and continue united from thence to the 
brain; so that the right optic nerve, after the 
meeting of the two nerves, is composed of the 
fibres, coming from the right side of both retina?, 
and the left, of the fibres coming from the left 
side of both retince? 

This is undoubtedly a curious and rational 
question; because, if we could find ground from 
anatomy to answer it in the affirmative, it would 
lead us a step forward in discovering the cause 
of the correspondence and sympathy which there 
is between certain points of the two retina;. For 
although we know not what is the particular 
function of the optic nerves, yet it is probable, 
that some impression made upon them, and com- 
municated along their fibres, is necessary to 
vision : And whatever be the nature of this im- 
pression, if two fibres are united into one, an im- 
pression made upon one of them, or upon both, 
may probably produce the same effect. Anato- 
mists think it a sufficient account of a sympathy 
between two parts of the body, when they are 
served by branches of the same nerve : we should 
therefore look upon it as an important discovery 



300 OF THE HUMAN MIND. [CHAP. 6. 

in anatomy, if it were found that the same nerve 
sent branches to the corresponding points of the 
retinae. 

But hath any such discovery been made ? No, 
not so much as in one subject, as far as I can 
learn. But in several subjects, the contrary 
seems to have been discovered. Dr. Forterfield 
hath given us two cases at length from Vesalius, 
and one from Cjesalpinus, wherein the optic 
nerves, after touching one another as usual, ap- 
peared to be reflected back to the same side 
whence they came, without any mixture of their 
fibres. Each of these persons had lost an eye 
some time before his death, and the optic nerve 
belonging to that eye was shrunk, so that it could 
be distinguished from the other at the place 
where they met. Another case which the same 
author gives from Vesalius, is still more remark- 
able ; for in it the optic nerves did not touch at 
all ; and yet, upon inquiry, those who were most 
familiar with the person in his life time, declar- 
ed that he never complained of any defect of sight, 
or of li Is seeing objects double. Djemerbroeck 
tells us, that Aquapendens and Valverda like- 
wise affirm, that they have met with subjects 
wherein the optic nerve did not touch. 

As these observations were made before Sir 
Tsaac Newton put this query, it is uncertain 
whether he was ignorant of them, or whether he 
suspected some inaccuracy in them, and desired 
that the matter might be more carefully examin- 
ed. But from the following passage of the most 



SECT. 19-] OF SEEING. SOL 

accurate Wjnslow, it does not appear, that later 
observations have been more favourable to his 
conjecture. " The union of these [optic] nerves, 
" by the small curvatures of their cornaa, is very 
" difficult to be unfolded in human bodies. This 
". union is commonly found to be very close, but 
" in some subjects it seems to be no more than a 
" strong adhesion, in others to be partly made 
" by an intersection or crossing of fibres. They 
" have been found quite separate; and in other 
" subjects, one of them has been found to be very 
" much altered both in size and colour, through 
" its whole passage, the other remaining in its na- 
" tural state." 

When we consider this conjecture of Sir Isaac 
Newton by itself, it appears more ingenious, and 
to have more verisimilitude, than any thing that 
lias been offered upon the subject; and we ad- 
mire the caution and modesty of the author, in 
proposing it only as a subject of inquiry: but when 
we compare it with the observations of anatomists 
which contradict it, we are naturally led to this 
reflection, That if we trust to the conjectures of 
men of the greatest genius in the operations of na- 
ture, we have only the chance of going wrong in 



an ingenious manner. 



The second part of the query is, Whether the 
two species of objects from the two eyes are not, 
at the place where the -optic nerves meet, united 
into one species or picture, half of which is car- 
ried thence to the sensorivm in the right optic 
nerve, and the other half in the left ? and whe- 



SO I OF THE HUMAN MIND. [CHAP. 6. 

ther these two halves are not so put together 
again at the sensorium, as to make one species or 
picture? 

Here it seems natural to put the previous ques- 
tion, What reason have we to believe, that pic- 
tures of objects are at all carried to the sensorium 
either by the optic nerves, or by any other nerves ? 
Is it not possible, that this great philosopher, as 
well as many of a lower form, having been led 
into this opinion at first by education, may have 
continued in it, because he never thought of call- 
ing it in question ? I confess this was my own 
case for a considerable part of my life. But since 
I was led by accident to think seriously what 
reason I had to believe it, 1 could find none at 
all. It seems to be a mere hypothesis, as much 
as the Indian philosopher's elephant. I am not 
conscious of any pictures of external objects in 
my sensorium, any more than in my stomach : the 
things which I perceive by my senses, appear to 
be external, and not in any part of the brain y 
and my sensations, properly so called, have no 
resemblance of external objects. 

The conclusion from all that hath been said 
in no less than seven sections, upon our seeing 
objects single with two eyes, is this, That by an 
original property of human eyes, objects painted 
upon the centres of the two retince, or upon points 
similarly situate with regard to the centres, ap- 
pear in the same visible place ; that the most 
plausible attempts to account for this property 
of the eyes, have been unsuccssefu! ; and there- 



SECT. 19.] OF SEEING. 303 

fore, that it must be either a primary law of our 
constitution, or the consequence of some more 
general law which is not yet discovered. 

We have now finished what we intended to say, 
both of the visible appearances of things to the 
eye, and of the laws of our constitution by which 
those appearances are exhibited. But it was ob- 
served, in the beginning of this chapter, that the 
visible appearances of objects serve only as signs 
of their distance, magnitude, figure, and other 
tangible qualities. The visible appearance, is that 
which is presented to the mind by nature, ac- 
cording to those laws of our constitution which 
have been explained. But the thing signified by 
that appearance, is that which is presented to the 
mind by custom. 

When one speaks to us in a language that is 
familiar, we hear certain sounds, and this is all 
the effect that his discourse has upon us by na- 
ture : but by custom we understand the meaning 
of these sounds ; and therefore we fix our attention 
not upon the sounds, but upon the thing signified, 
by them. In like manner, we see only the visible 
appearance of objects by nature ; but we learn 
by custom to interpret these appearances, and to 
understand their meaning. And when this visual 
language is learned, and becomes familiar, we at- 
tend only to the things signified ; and cannot, 
without great difficulty, attend to the signs by 
which they are presented. The mind passes 
from one to the other so rapidly, and so familiar- 
ly, that no trace of the sign is loft in the memory, 



301 OF THE HUMAN MIND. [CHAP. 6. 

and we seem immediately, and without the inter- 
vention of any sign, to perceive the thing signified. 

When I look at the apple-tree, which stands 
before my window, I perceive at the first glance, 
its distance and magnitude, the roughness of its 
trunk, the disposition of its branches, the figure 
of its leaves and fruit. I seem to perceive all 
these things immediately. The visible appearance 
which presented them all to the mind, has en- 
tirely escaped me ; I cannot, without great diffi- 
culty, and painful abstraction, attend to it, even 
when it stands before me. Yet it is certain, 
that this visible appearance only, is presented to 
my eye by nature, and that I learned by custom 
to collect all the rest from it. If I had never seen 
before now, I should not perceive either the dis- 
tance or tangible figure of the tree, and it would 
have required the practice of seeing for many 
months, to change that original perception which 
nature gave me by my eyes, into that which I 
now have by custom. 

The objects which we see naturally and origi- 
nally, as hath been before observed, have length 
and breadth, but no thickness, nor distance from 
the eye. Custom, by a kind of legerdemain, 
withdraws gradually these original and proper ob- 
jects of sight, and substitutes in their place objects 
of touch, which have length, breadth, and thick- 
ness, and a determinate distance from the eye. 
By what means this change is brought about, and 
what principles of the human mind concur in it, 
we are next to enquire. 



SECT. £0.] OF SEEING. 305 

SECT. XX. 

Of perception in general. 

Sensation, and the perception of external ob. 
jects by the senses, though very diffeient in their 
nature, have commonly been considered as one 
and the same thing. The purposes of common 
life do not make it necessary to distinguish them, 
and the received opinions of philosophers tend ra- 
ther to confound them ; but without attending 
carefully to this distinction, it is impossible to 
have any just conception of the operations of our 
senses. The most simple operations of the mind 
admit not of a logical definition : all we can do 
is to describe them so as to lead those who are 
conscious of them in themselves, to attend to 
them, and reflect upon them : and it is often very 
difficult to describe them so as to answer to this 
intention. 

The same mode of expression is used to denote 
sensation and perception ; and therefore we are 
apt to look upon them as things of the same na- 
ture. Thus, I feel a pain ; I see a tree : the first 
denoteth a sensation, the last a perception. — 
The grammatical analysis of both expressions is 
the same : for both consist of an active verb and 
an object. But if we attend to the things signified 
by these expressions, we shall find, that in the 
first, the distinction between the act and the ob- 

u 



306 OF THE HUMAN MIND. [CHAP. 6. 

ject is not real bat grammatical : in the second, 
the distinction is not only grammatical but real. 

The form of the expression, I feel pain, might 
seem to imply, that the feeling is something dis- 
tinct from the pain felt ; yet in reality, there is 
no distinction. As thinking a thought is an ex- 
pression which could signify no more than think- 
ing, so feeling a pain signifies no more than being 
pained. What we have said of pain is applicable 
to every other mere sensation. It is difficult to 
give instances, very few of our sensations having 
names ; and where they have, the name being 
common to the sensation, and to something else 
which is associated with it. But when we attend 
to the sensation by itself) and separate it from 
other things, which are conjoined with it in the 
imagination, it appears to be something which 
can have no existence but in a sentient mind, no 
distinction from the act of the mind by which it 
is felt. 

Perception, as w 7 e here understand it, hath al- 
ways an object distinct from the act by which 
it is perceived; an object which may exist whe- 
ther it be perceived or not. I perceive a tree 
that grows before my window; there is here an 
object which is perceived, and an act of the 
mind by which it is perceived ; and these two are 
not only distinguishable, but they are extremely 
unlike in their natures. The object is made up of 
a trunk, branches, and leaves; but the act of the 
mind, by which it is perceived, hath neither 
trunk, branches, nor leaves. I am conscious of 



SECT. 20.] OF SEEING. 307 

this act of my mind, and lean reflect upon it; 
but it is too simple to admit of an analysis, and I 
cannot find proper words to describe it. I find 
nottiing tlfat resembles it so much as the remem- 
brance of the tree, or the imagination of it. Yet 
both these differ essentially from perception ; they 
differ likewise one from another. It is in vain 
that a philosopher assures me, that the imagina- 
tion of the tree, the remembrance of it, and the 
perception of it, are all one, and differ only in 
degree of vivacity. I know the contrary ; for I 
am as well acquainted with all the three, as 1 am 
with the apartments of my own house. I know 
this also that the perception of an object implies 
both a conception of its form and a belief of its 
present existence. 1 know, moreover, that this 
belief is not the effect of argumentation and 
reasoning ; it is the immediate effect of my con- 
stitution. 

I am aware, that this belief which I have in 
perception, stands exposed to the strongest bat- 
teries of scepticism. But they make no great im- 
pression upon it. The sceptic asks me, Why 
do you believe the existence of the external ob- 
ject which you perceive? This belief, Sir, is none 
of my manufacture ; it came from the mint of 
nature ; it bears her image and superscription ; 
and, ifitisnot right, the fault is not mine: I 
even took it upon trust, and without suspicion. — 
Reason, says the sceptic, is the only judge of 
truth, and you ought to throw off every opinion 

and every belief that is not grounded on reason. 

u 2 



308 OF THE HUMAN MIND. CHAP. 0, 

Why, Sir, should I believe the faculty of reason 
more than that of perception ; they came both 
out of the same shop, and were made by the same 
artist; and if he puts one piece of false ware into 
my hands, what should hinder him from putting 
another ? 

Perhaps the sceptic will agree to distrust rea- 
son, rather than give any credit to perception, 
For, says he, since by your own concession, the 
object which you perceive, and that act of your 
mind, by which you perceive it, are quite differ- 
ent things, the one may exist without the other ; 
and as the object may exist without being per- 
ceived, so the perception may exist without an 
object. There is nothing so shameful in a philo- 
sopher as to be deceived and deluded ; and there- 
fore you ought to resolve firmly to withhold as- 
sent, and throw off this belief of external objects, 
which may be all delusion. For my part, I will 
never attempt to throw it off; and although the 
sober part of mankind will not be very anxious 
to know my reasons, yet if they can be of use 
to any sceptic, they are these. 

First, Because it is not in my power : why then 
should I make a vain attempt? It would be 
agreeable to fly to the moon, and to make a visit 
to Jupiter and Saturn ; but when I know that 
nature has bound me down by the law of gravita- 
tion to this planet which I inhabit, I rest content- 
ed, and quietly suffer myself to be carried along 
in its orbit. My belief is carried along by per- 
ception, as irresistibly as my body by the Earth* 






SECT. 20.] OF SEEING. 309 

And the greatest sceptic will find himself to be 
in the same condition. He may struggle hard 
to disbelieve the informations of his senses, as a 
man does to swim against the torrent ; but ah ! it 
is in vain. It is in vain that he strains every 
nerve, and wrestles with nature, and with every 
object that strikes upon his senses. For after all, 
when his strength is spent in the fruitless attempt, 
he will be carried down the torrent with the com- 
mon herd of believers. 

Secondly, I think it would not be prudent to 
throw off this belief, it it were in my power. If 
nature intended to deceive me, and impose upon 
me by false appearances, and I, by my great cun- 
ning and profound logic, have discovered the im- 
posture ; prudence would dictate to me in this 
case, even to put up this indignity done me, as 
quietly as I could, and not to call her an impos- 
tor to her face, lest she should be even with me 
in another way. For what do I gain by resent- 
ing this injury ? You ought at least not to be- 
lieve what she says. This indeed seems reason- 
able, if she intends to impose upon me. But what 
is the consequence ? I resolve not to believe my 
senses. I break my nose against a post that 
comes in my way : I step into a dirty* kennel ; 
and, after twenty such wise and rational actions, 
am taken up and clapt into a madhouse. Now, 
I confess I would rather make one of the credu- 
lous fools whom nature imposes upon, than of 
those wise and rational philosophers who resolve 
to withhold assent at all this expence. .If a man 



310 OF THE HUMAN MIND. [CHAP. 6. 

pretends to be a sceptic with regard to the infor- 
mations of sense, and yet prudently keeps out of 
harm's way as other men do, he must excuse my 
suspicion, that he either acts the hypocrite, or. 
imposes upon himself. For if the scale of his be- 
lief were so evenly poised, as to lean no more on 
one side than on the contrary, it is impossible that 
his actions could be directed by any rules of com- 
mon prudence. 

Thirdly, Although the two reasons already 
mentioned are perhaps two more than enough, I 
shall offer a third. I gave implicit belief to the 
informations of nature by my senses, for a con- 
siderable part of my life, before I had learned so 
much logic as to be able to start a doubt concern- 
ing them. And now, when I reflect upon what 
is past, I do not find that I have been imposed 
upon by this belief. I find, that without it I 
must have perished by a thousand accidents. 
1 find that without it I should have been no 
wiser now than when I was born. I should 
not even have been able to acquire that ' lo- 
gic which suggests these sceptical doubts with 
regard to my senses. Therefore, I consider 
this intuitive belief as one of the best gifts 
of nature. I thank the Author of my being 
who bestowed it upon me, before the eyes of my 
reason were opened, and still bestows it upon me 
to be my guide, where reason leaves me in the 
dark. And now I yield to the direction of my 
senses, not from instinct only, but from confi- 
dence and trust in a faithful and beneficent 



SECT. 20.] OF SEEING. 311 

Monitor, grounded upon the experience of his 
paternal care and goodness. 

In all this 1 deal with the Author of my being, 
no otherwise than I thought it reasonable to deal 
with my parents and tutors. I believed by in- 
stinct whatever they told me, long before 1 had 
the idea of a lie, or thought of the possibility of 
their deceiving me. Afterwards upon reflection, 
I found they had acted like fair and honest people 
who wished me well. I found, that if I had not 
believed what they told me, before I could give 
a reason of my belief, I had to this day been little 
better than a changeling. And although this na- 
tural credulity hath sometimes occasioned my 
being imposed upon by deceivers, yet it hath 
been of infinite advantage to me upon the whole ; 
therefore I consider it as another good gift of 
nature. And I continue to give that credit, from 
reflection, to those of whose integrity and vera- 
city 1 have had experience, which before I gave 
from instinct. 

There is a much greater similitude than is 
commonly imagined between the testimony of 
nature given by our senses, and the testimony of 
men given by language. The credit we give to 
both is at first the effect of instinct onlv. When 
we grow up, and begin to reason about them, 
the credit given to human testimony is restrained, 
and weakened, by the experience we have of de- 
ceit. But the credit given to the testimony of 
our senses, is established and confirmed by the 
uniformity and constancy of the laws of nature. — 



312 OF THE HUMAN MIND. [CHAP. 6. 

Our perceptions are of two kinds ; some are 
natural and original, others acquired, and the 
fruit of experience. When I perceive that this 
is the taste of cyder, that of brandy; and this is 
the smell of an apple, that of an orange ; that 
this is the noise of thunder, that the ringing' of 
bells ; this the sound of a coach passing, that the 
voice of such a friend ; these perceptions, and 
others of the same kind, are not original, they are 
acquired. But the perception which I have by 
touch, of the hardness and softness of bodies, of 
their extension, figure, and motion, is not acquired; 
it is original. 

In all our senses, the acquired perceptions are 
many more than the original, especially in sight. 
By this sense we perceive originally the visible 
figure and colour of bodies only, and their visible 
place : but we learn to perceive by the eye almost 
every thing which we can perceive by touch. 
The original perceptions of this sense, serve only 
as signs to introduce the acquired. 

The signs by which objects are presented to 
us in perception, are the language of nature to 
man ; and as, in many respects, it hath great af- 
finity with the language of man to man ; so par- 
ticularly in this, that both are partly natural and 
original, partly acquired by custom. Our origi- , 
nal or natural perceptions are analogous to the 
natural language of man to man, of which we 
took notice in the 4th chapter ; and our acquired 
perceptions are analogous to artificial language, 
which, in our mother tongue, is got very much 



SECT. 20.] OF SEEING. 313 

in the same manner with our acquired perceptions, 
as we shall afterwards more fully explain. 

Not only men, but children, idiots, and brutes, 
acquire by habit many perceptions which they 
had not originally. Almost every employment 
in life, hath perceptions of this kind that are pe- 
culiar to it. The shepherd knows every sheep 
of his flock, as we do our acquaintance, and can 
pick them out of another flock one by one. The 
butcher knows by sight the weight and quality of 
his beeves and sheep before they are killed. The 
farmer perceives by his eye, very nearly, the quan- 
tity of hay in a rick, or of corn in a heap. The 
sailor sees the burden, the build, and the distance 
of a ship at sea, while she is a great way off. — 
Every man accustomed to writing, distinguishes 
his acquaintance by their hand-writing, as he does 
by their faces. And the painter distinguishes in 
the works of his art, the style of all the great 
masters. In a word, acquired perception is very 
different in different persons, according to the 
diversity of objects about which they are employ- 
ed, and the application they bestow in observing 
them. 

Perception ought not only to be distinguished 
from sensation, but likewise from that knowledge 
of the objects of sense which is got by reasoning. 
There is no reasoning in perception, as hath been 
observed. The belief which is implied in it, is 
the effect of instinct. But there are many things, 
with regard to sensible objects, which we can in- 
fer from what we perceive ; and such conclusions 



314 OF THE HUMAN HIND. [CHAP. G. 

of reason ought to be distinguished from what is 
merely perceived. When I look at the moon, I 
perceive her to be sometimes circular, sometimes 
horned, and sometimes gibbous. Tiiis is simple 
perception, and is the same in the philosopher 
and in the clown: but from these various appear- 
ances of her enlightened part, I infer that she is 
really of a spherical figure. This conclusion is 
not obtained by simple perception, but by rea- 
soning. Simple perception has the same relation 
to the conclusions of reason drawn from our per- 
ceptions, as the axioms in mathematics have to 
the propositions. I cannot demonstrate, that two 
quantities which are equal to the same quantity, 
are equal to each other ; neither can I demon- 
strate, that the tree which I perceive exists. — 
But, by the constitution of my nature, my belief 
is irresistably carried along by my apprehension 
of the axiom ; and by the constitution of my na- 
ture, my belief is no less irresistably carried along 
by my perception of the tree. All reasoning is 
from principles. The first principles of mathe- 
matical reasoning are mathematical axioms and 
definitions \ and the first principles of all our 
reasoning about existences, are our perceptions. 
The first principles of every kind of reasoning- 
are given us by nature, and are of equal authori- 
ty with the faculty of reason itself, which is also 
the gift of nature. The conclusions of reason 
are all built upon first principles, and can have 
no other foundation. Most justly, therefore, do 
such principles disdain to be tried by reason, and 



SECT. 20.] OF SEEING. SI 5 

laugh at all the artillery of the logician, when it 
is directed against them. 

When a long train of reasoning is necessary in 
demonstrating a mathematical proposition, it is 
easily distinguished from an axiom, and they 
seem to be things of a very different nature. But 
there are some propositions which lie so near to 
axioms, that it is difficult to say, whether they 
ought to be held as axioms, or demonstrated as 
propositions. The same thing holds with regard 
to perception, and the conclusions drawn from it. 
Some of these conclusions follow our perceptions 
so easily, and are so immediately connected with 
them, that it is difficult to fix the limit which di- 
vides the one from the other. 

Perception, whether original or acquired, im- 
plies no exercise of reason ; and is common to 
men, children, idiots, and brutes. The more ob- 
vious conclusions drawn from our perceptions, 
by reason, make what we call comm.n understand- 
ing$ by which men conduct themselves in the 
common affairs of life, and by which they are dis- 
tinguished from idiots. The more remote con- 
clusions which are drawn from our perceptions 
by reason, make what we commonly call science 
in the various parts of nature, whether in agri- 
culture, medicine, mechanics, or in any part of 
natural philosophy. When I see a garden in 
good order, containing a great variety of things 
of the best kinds, and in the most most flourishing 
condition, I immediately conclude from these 
signs, the skill aud industry of the gardener. A 



Sl6 OF THE HUMAN MIND. [CHAP. 6. 

farmer when he rises in the morning, and per- 
ceives that the neighbouring brook overflows 
his field, concludes that a great deal of rain hath 
fallen in the night. Perceiving his fence broken 
and his corn trodden down, he concludes that 
some of his own or his neighbours cattle have broke 
loose. Perceiving that his stable-door is broke 
open and some of his horses gone, he concludes 
that a theif hath carried them off. He traces the 
prints of his horses feet in the soft ground, and 
by them discovers which road the thief hath tak- 
en. These are instances of common understand- 
ing, which dwells so near to perception, that it 
is difficult to trace the line which divides the one 
from the other. In like manner, the science of 
nature dwells so near to common understanding, 
that we cannot discern where the latter ends and 
the former begins. I perceive that bodies 
lighter than water, swim in water, and that 
those which are heavier sink. Hence, I con- 
clude, that if a body remains wherever it is 
put under water, whether at the top or bottom, 
it is precisely of the same weight with water. If 
it will rest only when part of it is above water, it 
is lighter than water. And the greater the part a- 
bove water is compared with the whole, the lighter 
is the body. If it had no gravity at all, it would 
make no impression upon the water, but stand 
wholly above it. Thus, every man, by common 
understanding, has a rule by which he judges of 
the specific gravity of bodies which swim in wa- 
ter : and a step or two more leads him into the 
science of hydrostatics. 



SECT. 21.] OF SEEING. 317 

All that we know of nature, or of existences, 
may be compared to a tree, which hath its root, 
trunk, and branches. In this tree of knowledge, 
perception is the root, common understanding is 
the trunk, and the sciences are the branches. 



SECT. XXI. 

Of the process of Nature in perception. 

Although there is no reasoning in perception, 
yet there are certain means and instruments, 
which, by the appointment of nature, must inter- 
vene between the object and our perception of it ; 
and, by these our perceptions are limited and re- 
gulated. First, If the object is not in contact 
with the organ of sense, there must be some me- 
dium which passes between them. Thus, in vi- 
sion, the rays of light ; in hearing, the vibrations 
of elastic air; in smelling the effluvia of the body 
smelled, must pass from the object to the organ ; 
otherwise we have no perception. Secondly, 
There must be some action or impression upon 
the organ of sense, either by the immediate ap- 
plication of the object, or by the medium that 
goes between them. Thirdly, The nerves which 
go from the brain to the organ, must receive some 
impression by means of that which was made 
upon the organ ; and probably, by means of the 
nerves, some impression must be made upon the 



313 OF THE HUMAN MIND. [CHAP. 6. 

brain. Fourthly, The impression made upon the 
organ, nerves, and brain, is followed by a sensa- 
tion. And, last of all, This sensation is followed 
by the perception of the object. 

Thus our perception of objects is the result of a 
train of operations ; some of which affect the body 
only, others affect the mind. We know very little 
of the nature of some of these operations; we 
know not at all how they are connected together, 
or in what way they contribute to that perception 
which is the result of the whole : but, by the laws 
of our constitution, we perceive objects in this, 
and in no other way. 

There may be other beings, who can conceive 
external objects without rays of light, or vibra- 
tions of air, or effluvia of bodies, without impres- 
sions on bodily organs, or even without sensations: 
but w r e are so framed by the Author of nature, 
that even when we are surrounded by external 
objects, we may perceive none of them. Our 
faculty of perceiving an object lies dormant, un- 
til it is roused and stimulated by a certain corre- 
sponding sensation. Nor is this sensation always 
at hand to perform its office ; for it enters into the 
mind only in consequence of a certain correspond- 
ing impression made on the organ of sense by the 
object. 

Let us trace this correspondence of impres- 
sions, sensations, and perceptions, as far as we 
can ; beginning with that which is first in order, 
the impression made upon the bodily organ.— 
But, alas! we know not of what nature these im- 



SECT. -IS.] OF SEEING. 319 

pressions are, far less how they excite sensations 
in the mind. 

We know that one body may act upon another 
by pressure, by percussion, by attraction, by re- 
pulsion, and probably in many other ways, which 
we neither know, nor have names to express, 
But in which of these ways objects, when per- 
ceived by us, act upon the organs of sense, these 
organs upon the nerves, and nerves upon the 
brain, we know not. Can any man tell me how, 
in vision, the rays of light act upon the retina t 
how the retina acts upon the optic nerve, and 
how the optic nerve acts upon the brain ? No 
man can. When T feel the pain .of the gout in 
my toe, I know that there is some unusual im- 
pression made upon that part of my body. But 
of what kind is it ? Are the small vessels distend- 
ed with some redundant elastic or unelastic 
fluid ? Are the fibres unusually stretched? Are 
they torn asunder by force, or gnawed and cor- 
roded by some acrid humour? I can answer none 
of these questions. All that I feel, is pain, which 
is not an impression upon the body, but upon the 
mind ; and all that I perceive by this sensation 
is, that some distemper in my toe occasions this 
pain. But as I know not the natural temper and 
texture of my toe when it is at ease, I know as 
little what change or disorder of its parts occasions 
this uneasy sensation. In like manner, in every 
other sensation, there is, without doubt, some im- 
pression made upon the organ of sense ; but an im- 
pression of which we know not the nature. It is 



820 OF THE HUMAN MIND. [CHAP. 6. 

too subtile to be discovered by our senses, and 
we may make a thousand conjectures without com- 
ing near the truth. If we understood the struc- 
ture of our organs of sense so miuutely, as to dis- 
cover what effects are produced upon them by ex- 
ternal objects, this knowledge would contribute 
nothing to our perception of the object; for they 
perceive as distinctly who know least about the 
manner of perception, as the greatest adepts. It 
is necessary that the impression be made upon 
our organs, but not that it be known. Nature 
carries on this part of the process of perception 
without our consciousness or concurrence. 

But we cannot be unconscious of the next step 
in this process, the sensation of the mind, which 
always immediately follows the impression made 
upon the body. It is essential to a sensation to 
be felt, and it can be nothing more than we feel 
it to be. W we can only acquire the habit of at- 
tending to our sensations, we may know them 
perfectly. But how are the sensations of the 
mind produced by impressions upon the body ? 
Of this we are absolutely ignorant, having no 
means of knowing how the body acts upon the 
mind, or the mind upon the body. When we 
consider the nature and attributes of both, they 
seem to be so different, and so unlike, that we 
can find no handle by which the one may lay hold 
of the other. There is a deep and dark gulph 
between them, which our understanding cannot 
pass ; and the manner of their correspondence 
and intercourse is absolutely unknown. 



SECT. 21.] OF SEEING. 321 

Experience teaches us, that certain impressions 
upon the body are constantly followed by certain 
sensations of the mind ; and that, on the other 
hand, certain determinations of the mind are 
constantly followed by certain motions in the bo- 
dy; but we see not the chain that ties these things 
together. Who knows but their connection may 
be arbitrary, and owing to the will of our Maker? 
Perhaps the same sensations might have been 
connected with other impressions or other bodily 
organs. Perhaps we might have been so made 
as to taste with our fingers, to smell with our ears, 
and to hear by the nose. Perhaps we might have 
been so made, as to have all the sensations and 
perceptions which we have, without any impres- 
sion made upon our bodily organs at all. 

However these things may be, if nature had 
given us nothing more than impressions made 
upon the body, and sensations in our mind cor- 
responding to them, we should in that case have 
been merely sentient, but not percipient beings. 
We should never have been able to form a con- 
ception of any external object, far less a belief of 
its existence. Our sensations have no resem- 
blance to external objects ; nor can we discover, 
by our reason, any necessary connection between 
the existence of the former, and that of the lat* 
ter. 

We might perhaps have been made of such a 
constitution, as to have our present perceptions 
connected with other sensations. We might per- 
haps have had the perception of external objects 



322 OF THE HUMAN MIND. [CHAP. 6. 

without either impressions upon the organs of 
sense, or sensations. Or, lastly, The perceptions 
we have, might have been immediately connect- 
ed with the impressions upon our organs, without 
any intervention of sensations. This last seems 
really to be the case in one instance, to wit, in 
our perception of the visible figure of bodies, as 
was observed in the 8th section of this chapter. 

The process of nature in perception by the 
senses may therefore be conceived as a kind of 
drama, wherein some things are performed be- 
hind the scenes, others are represented to the 
mind in different scenes, one succeeding another. 
The impression made by the object upon the 
organ, either by immediate contact, or by some 
intervening medium, as well as the impression 
made upon the nerves and brain, is performed 
behind the scenes, and the mind sees nothing of 
it. But every such impression, by the laws of 
the drama, is followed by a sensation, which is 
the first scene exhibited to the mind ; and this 
scene is quickly succeeded by another, which is 
the perception of the object. 

In this drama, nature is the actor, we are the 
spectators. We know nothing of the machinery 
by means of which every different impression 
upon the organ, nerves, and brain, exhibits its 
corresponding sensation ; or of the machinery by 
means of which each sensation exhibits its corre- 
sponding perception. We are inspired with the 
sensation, and we are inspired with the corre- 
sponding perception, by means unknown. And 



SECT. 21.] OF SEEING. 323 

because the mind passes immediately from the 
sensation to that conception and belief of the ob- 
ject which we have in perception, in the same 
manner as it passes from signs to the things sig- 
nified by them, we have therefore called our sen- 
sations signs of external objects; finding no word 
more proper to express the function which nature 
hath assigned them in perception, and the rela- 
tion which they bear to their corresponding ob- 
jects. 

There is no necessity of a resemblance between 
the sign and the thing signified : and indeed no 
sensation can resemble any external object. But 
there are two things necessary to our knowing- 
things by means of signs. First, That a real 
connection between the sign and the thing signi- 
fied be established, either by the course of na- 
ture, or by the will and appointment of men. 
When they are connected by the course of nature, 
it is a natural sign ; when by human appoint- 
ment, it is an artificial sign. Thus, smoke is a 
natural sign of fire ; certain features are natural 
signs of anger : but our words, whether express- 
ed by articulate sounds or by writing, are artifi- 
cial signs of our thoughts and purposes. 

Another requisite to our knowing things by 
signs is, that the appearance of the sign to the 
mind, be followed by the conception and belief 
of the thing signified. Without this, the sign is 
not understood or interpreted ; and therefore is 
no sign to us, however fit in its own nature for 
that purpose. 

X 2 



32b OF THE HUMAN MIND. [CHAP. (5. 

Now, there are three ways in which the mind 
passes from the appearance of a natural sign to 
the conception and belief of the thing signified - r 
by original principles of our constitution, by cus- 
tom, and by reasoning. 

Our original perceptions are got in the first of 
these ways, our acquired perceptions in the se- 
cond, and all that reason discovers of the course 
of nature, in the third. In the first of these 
ways, nature, by means of the sensations of touch, 
informs us of the hardness and softness of bodies ; 
of their extension, figure, and motion ; and of 
that space in which they move and are placed, as 
hath already been explained in the fifth chapter 
of this Inquiry. And in the second of these ways 
she informs us*, by means of our eyes, of almost 
all the same things which originally we could per- 
ceive only by touch. 

In order, therefore, to understand more parti- 
cularly how we learn to perceive so many things 
by the eye, which originally could be perceived 
only by touch, it will be proper, first, To point 
out the signs by which those things are exhibited 
to the eye, and their connection with the things 
signified by them ; and, secondly, To consider 
how the experience of this connection produces 
that habit by which the mind, without any rea- 
soning or reflection, passes from the sign to the 
conception and belief of the thing signified. 

Of all the acquired perceptions which we have 
by sight, the most remarkable is the perception 
of the distance of objects from the eye \ we shall 



SECT. 22.] OF SEEING. 325 

therefore particularly consider the signs by which 
this perception is exhibited, and only make some 
general remarks with regard to the signs which 
are used in other acquired perceptions. 



SECT. XXII, 



Of the signs by which we learn to perceive distance 
Jrom the eye. 

It was before observed in general, That the ori- 
ginal perceptions of sight are signs which serve 
to introduce those that are acquired : but this is 
not to be understood as if no other signs were 
employed for that purpose. There are several 
motions of the eyes, which, in order to distinct 
vision, must be varied, according as the object is 
more or less distant; and such motions being by 
habit connected with the corresponding distances 
of the object, become signs of those distances. 
These motions were at first voluntary and uncon- 
fhied ; but as the intention of nature was, to pro- 
duce perfect and distinct vision by their means, 
we soon learnt by experience to regulate them ac- 
cording to that intention only, without the least 
reflection. 

A ship requires a different trim for every varia- 
tion of the direction and strength of the wind ; 
and. if we may be allowed to borrow that word, 
the eyes require a different trim for every degree 



326 OF THE HUMAN MIND. [CHAP. G, 

of light, and for every variation of the distance 
of the object, while it is within certain limits. 
The eyes are trimmed for a particular object, by 
contracting certain muscles, and relaxing others j 
as the ship is trimmed for a particular wind, by 
drawing certain ropes and slackening others. The 
sailor learns the trim of his ship, as we learn the 
trim of our eyes, by experience. A ship, although 
the noblest machine that human art can boast, is 
far inferior to the eye in this respect, that it re- 
quires art and ingenuity to navigate her; and a 
sailor must know what ropes he must pull, and 
what he must slacken, to fit her to a particular 
wind : but with such superior wisdom is the fa- 
bric of the eye, and the principles of its motion 
contrived, that it requires no art or ingenuity to 
see by it. Even that part of vision which is got 
by experience, is attained by idiots. We need 
not know what muscles we are to contract, and 
what we are to relax, in order to fit the eye to a 
particular distance of the object. 

But although we are not conscious of the mo- 
tions we perform, in order to fit the eyes to the 
distance of the object, we are conscious of the 
effort employed in producing these motions ; and 
probably have some sensation which accompanies 
them, to which we give as little attention as to 
other sensations. And thus, an effort consciously 
exerted, or a sensation consequent upon that ef- 
fort, comes to be conjoined with the distance of 
the object which gave occasion to it, and by this 
conjunction becomes a sign of that distance. 



SECT. 22.] OF SEEING. 327 

Some instances of this will appear in considering 
the means or signs by which we learn to see the 
distance of objects from the eye. In the enumer- 
ation of these, we agree with Dr. Porterfield, 
notwithstanding that distance from the eye, in his 
opinion, is perceived originally, but in our opin- 
ion, by experience only. 

In general, when a near object affects the eye 
in one manner, and the same object, placed at a 
greater distance, affects it in a different manner; 
these various affections of the eye become signs 
of the corresponding distances. The means of 
perceiving distance by the eye, will therefore be 
explained, by shewing, in what various ways ob- 
jects affect the eye differently, according to their 
proximity or distance. 

1. It is well known, that to see objects distinct- 
ly at various distances, the form of the eye must 
undergo some change. And nature hath given 
us the power of adapting it to near objects, by 
the contraction of certain muscles, and to distant 
objects, by the contraction of other muscles. As 
to the manner in which this is done, and the 
muscular parts employed, anatomists do not alto- 
gether agree. The ingenious Dr. Jurin, in his 
excellent essay on distinct and indistinct vision, 
seems to have given the most probable account of 
this matter ; and to him I refer the reader. 

But whatever be the manner in which this 
change of the form of the eye is effected, it is 
certain that young people have commonly the 
power of adapting their eyes to all the distances 



328 OF THE HUMAN MIND. CHAP. 6. 

of the object, from six to seven inches to fifteen 
or sixteen feet ; so as to have perfect and distinct 
vision at any distance within these limits. From 
this it follows, that the effect we consciously em- 
ploy to adapt the eye to any particular distance 
of objects within these limits, will be connected 
and associated with that distance, and will become 
a sign of it. When the object is removed beyond 
the farthest limit of distinct vision, it will be seen 
distinctly ; but more or less so, according as its 
distance is greater or less : so that the degrees of 
indistinctness of the object may become the signs 
of distances considerably beyond the farthest li- 
mit of distinct vision. 

If we had no other mean but this of perceiving 
distance of visible objects, the most distant would 
not appear to be above twenty or thirty feet from 
the eye, and the tops of houses and trees would 
seem to touch the clouds; for in that case the 
signs of all greater distances being the same, they 
have the same signification, and give the same 
perception of distance. 

But it is of more importance to observe, that 
because the nearest limit of distinct vision in the 
time of youth, when we learn to perceive distance 
by the eye, is about six or seven inches, no object 
seen distinctly ever appears to be nearer than 
six or seven inches from the eye. We can, by 
art, make a small object appear distinct, when it 
is in reality not above half an inch from the eye; 
either by using a single microscope, or by look- 
ing through a small pin-hole in a card. Vvhen 



sect. 2:2.] OF SEEING. 329 

by either of these means, an object is made to 
appear distinct, however small its distance is in 
reality, it seems to be removed at least to the 
distance of six or seven inches, that is, within 
the limits of distinct vision. 

This observation is the more important, be- 
cause it affords the only reason we can give why 
an object is magnified either by a single micro- 
scope, or by being seen through a pin hole ; and 
the only mean by which we can ascertain the de- 
gree in which the object will be magnified by 
either. Thus, if the object is really half an inch 
distant from the eye, and appears to be seven 
inches distant, its diameter will seem to be en- 
larged in the same proportion as its distance, that 
is, fourteen times. 

2. In order to direct both eyes to an object, 
the optic axes must have a greater or less incli- 
nation, according as the object is nearer or more 
distant. And although we are not conscious of 
this inclination, yet we are conscious of the effort 
employed in it. £y this mean we perceive small 
distances more accurately than we could do bv 
the conformation of the eye only. And there- 
fore, we find, that those who have lost the sight 
of one eye, are apt, even within arm's-length, to 
make mistakes in the distance of objects, which 
are easily avoided by those who see with both eye?. 
Such mistakes are often discovered in snuffin^ a 
candle, in threading a needle, or in filling a tea- 
cup. 

When a picture is seen with both eyes, and at 



830 OF THE HUMAN MIND. [CHAP. G, 

no great distance, the representation appears not 
so natural as when it is seen only with one. The 
intention of painting being to deceive the eye, 
and to make things appear at different distances, 
which in reality are upon the same piece of can- 
vas, this deception is not so easily put upon both 
eyes as upon one ; because we perceive the dis- 
tance of visible objects more exactly and deter- 
minately with two eyes than with one. If the 
shading and relief be executed in the best man- 
ner, the picture may have almost the same ap- 
pearance to one eye as the objects themselves 
would have, but it cannot have the same appear- 
ance to both. This is not the fault of the artist, 
but an unavoidable imperfection in the art. And 
it is owing to what we just now observed, that 
the perception we have of the distance of objects 
by one eye is more uncertain, and more liable to 
deception, than that which we have by both. 

The great impediment, and I think the only 
invincible impediment, to that agreeable decep- 
tion of the eye which the painter aims at, is the 
perception which we have of the distance of vi- 
sible objects from the eye, partly by means of 
the conformation of the eye, but chiefly by means 
of the inclination of the optic axes. If this per- 
ception could be removed, I see no reason why 
a picture might not be made so perfect as to de- 
ceive the eye in reality, and to be mistaken for 
the original object. Therefore, in order to judge 
of the merit of a picture, we ought, as much as 
possible, to exclude these two means of perceiv* 
ing the distance of the several parts of it. 



SECT. 22.] OF SEEING. 331 

In order to remove this perception of distance, 
the connoisseurs in painting use a method which 
is very proper. They look at the picture with 
one eye, through a tube which excludes the view 
of all other objects. By this method, the princi- 
pal mean whereby we perceive the distance of 
the object, to wit, the inclination of the optic 
axes, is entirely excluded. I would humbly pro- 
pose, as an improvement of this method of view- 
ing pictures, that the aperture of the tube next 
to the eye should be very small. If it is as small 
as a pin-hole, so much the better, providing there 
be light enough to see the picture clearly. The 
reason of this proposal is, that when we look at 
an object through a small aperture, it will be seen 
distinctly, whether the conformation of the eye 
be adapted to its distance or not, and we have no 
means left to judge of the distance, but the light 
and colouring, which are in the painter's power. 
If, therefore, the artist performs his part proper- 
ly, the picture will by this method affect the eye, 
in the same manner that the object represented 
would do ; which is the perfection of this art. 

Although this second mean of perceiving the 
distance of visible objects be more determinate 
and exact than the first, yet it hath its limits, be- 
yond which it can be of no use. For when the 
optic axes directed to an object are so nearly 
parallel, that in directing them to an object yet 
more distant, we are not conscious of any new 
effort, nor have any different sensation, there our 
perception of distance stops j and as all more 



832 OF THE HUMAN MIND. [CHAP. 6* 

distant objects affect the eye in the same manner 
we perceive them to be at the same distance. — 
This is the reason why the sun, moon, planets, 
and fixed stars, when seen not near the horizon, 
appear to be all at the same distance, as if they 
touched the concave surface of a great sphere. 
The surface of this celestial sphere is at that dis- 
tance beyond which all objects affect the eye in 
the same manner. Why this celestial vault ap- 
pears more distant towards the horizon, than to- 
wards the zenith, will afterwards appear. 

3. The colours of objects, according as they 
are more distant, become more faint and languid, 
and are tinged more with the azure of the inter- 
vening atmosphere : to this we may add, that 
their minute parts become more indistinct, and 
their outline less accurately defined. It is by 
these means chiefly, that painters can represent 
objects at very different distances, upcn the same 
canvas. And the diminution of the magnitude 
of an object, would not have the effect of making 
it appear to be at a great distance without this 
degradation of colour, and indistinctness of the 
outline, and of the minute parts. If a painter 
should make a human figure ten times less than 
other human figures that are in the same piece, 
having the colours as bright, and the outline and 
minute parts as accurately defined, it would not 
have the appearance of a man at a g v eat distance, 
but of a pigmy or Lilliputian. 

When an object hath a known variety of co- 
lours, its distance is more clearly indicated by the 



SECT. 22.] OF SEEING. 333 

gradual dilution of the colours into one another, 
than when it is of one uniform colour. In the 
steeple which stands before me at a small distance 
the joinings of the stones are clearly perceptible ; 
the grey colour of the stone, and the white cement, 
are distinctly limited : when I see it at a greater 
distance, the joinings of the stones are less distinct, 
and the colours of the stone and of the cement 
begin to dilute into one another; at a distance 
still greater, the joinings disappear altogether, 
and the variety of colour vanishes. 

In an apple tree which stands at the distance 
of about twelve feet covered with flowers, I can 
perceive the figure and the colour of the leaves 
and petals ; pieces of branches, some larger, 
others smaller, peeping through the interval of 
the leaves, some of them enlightened by the sun's 
rays, others shaded ; and some openings of the 
sky are perceived through the whole. When I 
gradually remove from this tree, the appearance, 
even as to colour, changes every minute. First, 
the smaller parts, and the larger, are gradually 
confounded and mixed. The colours of leaves, 
petals, branches, and sky, are gradually diluted 
into each other, and the colour of the whole be- 
comes more and more uniform. This change of 
appearance, corresponding to the several dis- 
tances, marks the distance more exactly than it* 
the whole object had been of one colour. 

Dr. Smith, in his Optics, gives us a very cu- 
rious observation made by Bishop Berkeley, in 
his travels through Italy and Sicily. He observed, 
That in those countries, cities and palaces seen 



334 OF THE HUMAN MIND. [ CHAP * 6. 

at a great distance, appeared nearer to him by 
several miles than they really were : and he very 
judiciously imputed it to this cause, that the pu- 
rity of the Italian and Sicilian air, gave to very 
distant objects that degree of brightness and dis- 
tinctness which, in the grosser air of his own 
country, was to be seen only in those that are 
near. The purity of the Italian air has been as- 
signed as the reason why the Italian painters 
commonly give a more lively colour to the sky 
than the Flemish. Ought they not, for the same 
reason, to give less degradation of the colours, 
and less indistinctness of the minute parts, in the 
representation of very distinct objects ? 

It is very certain, that as, in air uncommonly 
pure, we are apt to think visible objects nearer, 
and less than they really are ; so, in air uncom- 
monly foggy, we are apt to think them more dis- 
tant, and larger than the truth. Walking by the 
sea-side in a thick fog, I see an object which 
seems to me to be a man on horseback, and at 
the distance of about half a mile. My companion, 
who has better eyes, or is more accustomed to see 
such objects in such circumstances, assures me, 
that it is a sea-gull, and not a man on horseback. 
Upon a second view, I immediately assent to his 
opinion ; and now it appears to me to be a sea- 
gull, and at the distance only of seventy or eighty 
yards. The mistake made on this occasion, and 
the correction of it, are both so sudden, that we 
are at a loss whether to call them by the name of 
judgment, or by that of simple perception. 

It is not worth while to dispute about names ; 



SECT. 22.] OF SEEING. 335 

but it is evident, that my belief, both first and 
last, was produced rather by signs than by argu- 
ments ; and that the mind proceeded to the con- 
clusion in both cases by habit, and not by ratio- 
cination. And the process of the mind seems to 
have been this. First, not knowing, or not 
minding, the effect of a foggy air on the visible 
appearance of objects, the object seems to me to 
have that degradation of colour, and that indis- 
tinctness of the outline, which objects have at 
the distance of half a mile; therefore, from the 
visible appearance as a sign, I immediately pro- 
ceed to the belief, that the object is half a mile 
distant. Then, this distance, together with the 
visible magnitude, signify to me the real magni- 
tude, which, supposing the distance to be half a 
mile, must be equal to that of a man on horse- 
back. Thus the deception is brought about. 
But when I am assured that it is a sea-gull, 
the real magnitude of a sea-gull, together with 
the visible magnitude presented to the eye, 
immediately suggest the distance, which in this 
case cannot be above seventy or eighty yards ; 
the indistinctness of the figure likewise sug- 
gests the fogginess of the air as its cause : 
and now the whole chain of signs, and things 
signified, seems stronger and better connected 
than it was before ; the half mile vanishes to 
eighty yards; the man on horseback dwindles to 
a sea-gull ; I get a new perception, and wonder 
how I got the former, or what is become of it ; 
for it is now so entirely gone, that I cannot re- 
cover it. 



335 OF THE HUMAN MIND. [cHAP. 6, 

It ought to be observed, that in order to pro- 
duce such deceptions from the clearness or fog- 
giness of the air, it must be uncommonly clear, 
or uncommonly foggy; for we learn from expe- 
rience, to make allowance for that variety of con- 
stitutions of the air which we have been accus- 
tomed to observe, and of which we are aware. 
Bishop Berkeley therefore committed a mistake, 
when he attributed the large appearance of the 
horizontal moon to the faintness of her light, oc- 
casioned by its passing through a larger tract of 
atmosphere : for we are so much accustomed to 
see the moon in all degrees of faintness and 
brightness, from the greatest to the least, that we 
learn to make allowance for it ; and do not ima- 
gine her magnitude increased by the faintness of 
her appearance. Besides, it is certain, that the 
horizontal moon, seen through a tube which 
cuts off the view of the interjacent ground, and 
of all terrestrial objects, loses all that unusual ap- 
pearance of magnitude. 

4. We frequently perceive the distance of ob- 
jects, by means of intervening or contiguous ob- 
jects, whose distance or magnitude is otherwise 
known. When I perceive certain fields or tracts 
of ground to lie between me and an object, it is evi- 
dent that these may become signs of its distance. 
And although we have no particular information 
of the dimensions of such fields or tracts, yet 
their similitude to others which we know, sug- 
gests their dimensions. 

We are so much accustomed to measure with 
our eye the ground which we travel, and to com- 



SECT. 22.] OF SEEING. 337 

pare the judgments of distances formed by sight, 
with our experience or information, that we learn 
by degrees, in this way to form a more accurate 
judgment of the distance of terrestrial objects, 
than we could do by any of the means before 
mentioned. An object placed upon the top of a 
high building appears much less than when plac- 
ed upon the ground at the same distance. When 
it stands upon the ground, the intervening tract 
of ground serves as a sign of its distance; and 
the distance, together with the visible magnitude, 
serves as a sign of its real magnitude. But when 
the object is placed on high, this sign of its dis- 
tance is taken away : the remaining signs lead 
us to place it at a less distance ; and this less 
distance, together with the visible magnitude, 
becomes a sign of a less real magnitude. 

The two first means we have mentioned, would 
never of themselves make a visible object appear 
above a hundred and fifty, or two hundred feet, 
distant ; because, beyond that there is no sensible 
change, either of the conformation of the eyes, 
or of the inclination of their axes. The third 
mean, is but a vague and undeterminate sign, 
when applied to distances above two or three 
hundred feet, unless we know the real colour and 
figure of the object ; and the fifth mean, to be 
afterwards mentioned, can only be applied to ob- 
jects which are familiar, or whose real magnitude 
is known. Hence it follows, that when unknown 
objects, upon, or near the surface of the earth, 
are perceived to be at the distance of some miles, 



338 OF THE HUMAN MIND. £ CHAP. 6. 

it is always by this fourth mean that we are led 
to that conclusion. 

Dr. Smith hath observed, very justly, that the 
known distance of the terrestrial objects which 
terminate our view, makes that part of the sky 
which is towards the horizon, appear more distant 
than that which is towards the zenith. Hence it 
comes to pass, that the apparent figure of the sky, 
is not that of a hemisphere, but rather a less seg- 
ment of a sphere. And hence likewise it comes 
to pass, that the diameter of the sun or moon, or 
the distance between two fixed stars, seen con- 
tiguous to a hill, or to any distant terrestrial ob- 
ject, appears much greater than when no such 
object strikes the eye at the same time. 

These observations have been sufficiently ex- 
amined and confirmed by Dr. Smith. I beg leave 
to add, that when the visible horizon is terminat- 
ed by very distant objects, the celestial vault 
seems to be enlarged in all its dimensions. When 
I view it from a confined street or lane, it bears 
some proportion to the buildings that surround 
me : but when I view it from a large plain, ter- 
minated on all hands by hills which rise one above 
another, to the distance of twenty miles from the 
eye, methinks I see a new heaven, whose mag- 
nificence declares the greatness of its Author, and 
puts every human edifice out of countenance; for 
now the lofty spires and the gorgeous palaces 
shrink into nothing before it, and bear no more 
proportion to the celestial dome, than their mak- 
ers bear to its Maker, 



SECT. 22.] OF SEEING. 339 

5, There remains another mean by which we 
perceive the distance of visible objects, and that 
is, the diminution of their visible or apparent 
magnitude. By experience, I know what figure 
a man, or any other known object, makes to my 
eye at the distance of ten feet : I perceive the 
gradual and proportional diminution of this visible 
figure, at the distance of twenty, forty, a hundred 
feet, and at greater distances, until it vanish al- 
together. Hence a certain visible magnitude of 
a known object, becomes the sign of a certain 
determinate distance, and carries along with it 
the conception and belief of that distance. 

In this process of the mind, the sign is not a 
sensation ; it is an original perception. We per- 
ceive the visible figure and visible magnitude of 
the object by the original powers of vision: but 
the visible figure is used only as a sign of the 
real figure, and the visible magnitude is used on- 
ly as a sign either of the distance, or of the real 
magnitude of the object ; and therefore these ori- 
ginal perceptions, like other mere signs, pass 
through the mind without any attention or re- 
flection. 

This last mean of perceiving the distance of 
known objects, serves to explain some very re- 
markable phenomena in optics, which would 
otherwise appear very mysterious. When we 
view objects of known dimensions through op- 
tical glasses, there is no other mean left of de- 
termining their distance, but this fifth. Hence 
it follows, that known objects seen through glas- 

y 2 



340 OF THE HUMAN MIND. [CHAP. 6 

ses, must seem to be brought nearer, in proportion 
to ti.e magnifying power of the glass, or to be 
removed to a greater distance, in proportion to 
the diminishing power of the glass. 

If a man who had never before seen objects 
through a telescope, were told, that the tele- 
scope which he is about to use, magnifies the di- 
ameter of the object ten times ; when he looks 
through this telescope at a man six feet high, what 
would he expect to see ? Surely he would very 
naturally expect to see a giant sixty feet high. 
But he sees no such thing. The man appears no 
more than six feet high, and consequently no 
bigger than he really is ; but he appears ten times 
nearer than he is. The telescope indeed magni- 
fies the image of this man upon the retina ten 
times in diameter, and must therefore magnify 
his visible figure in the same proportion ; and as 
we have been accustomed to see him of this visi- 
ble magnitude, when he was ten times nearer 
than he is presently, and in no other case ; this 
visible magnitude, therefore, suggests the concep- 
tion and belief of that distance of the object with 
which it hath been always connected. We have 
been accustomed to conceive this amplification of 
the visible figure of a known object only as the 
effect or sign of its being brought nearer: and we 
have annexed a certain determinate distance to 
every degree of visible magnitude of the object 5 
and therefore, any particular degree of visible 
magnitude, whether seen by the naked eye or by 
glasses, brings along with it the conception and 



SECT. 22.] OF SEEING, 34-1 

belief of the distance which corresponds to it. 
This is the reason why a telescope seems not to 
magnify known objects, but to bring them nearer 
to the eye. 

When we look through a pin-hole, or a single 
microscope, at an object which is half an inch 
from the eye, the picture of the object upon the 
retina is not enlarged, but only rendered distinct ; 
neither is the visible figure enlarged : yet the ob- 
ject appears to the eye twelve or fourteen times 
more distant, and as mauy times larger in diame- 
ter, than it really is. Such a telescope as we 
have mentioned, amplifies the image on the 
retina, and the visible figure ofj the object, ten 
times in diameter, and yet makes it seem no big- 
ger, but only ten times nearer. These appear- 
ances had been long observed by the writers on 
optics ; they tortured their invention to find the 
causes of them from optical principles ; but in 
vain: they must be resolved into habits of per- 
ception, which are acquired by custom, but are 
apt to be mistaken for original perceptions. The 
Bishop of Cloyne first furnished the world with 
the proper key for opening up these mysterious 
appearances ; but he made considerable mistakes 
in the application of it. Dr. Smith, in his ela- 
borate and judicious treatise of Optics, hath ap- 
plied it to the apparent distance of objects seen 
with glasses, and to the apparent figure of the 
heavens, with such happy success, that there can 
be no more doubt about the causes of these phe* 
nomena. 



34f2 OF THE HUMAN MIND. CHAP. 6. 

SECT. XXIII. 

Of the signs used in other acquired perceptions. 

The distance of objects from the eye, is the most 
important lesson in vision. Many others are 
easily learned in consequence of it. The dis- 
tance of the object, joined with its visible magni- 
tude, is a sign of its real magnitude : and the dis- 
tance of the several parts of an object, joined with 
its visible figure, becomes a sign of its real figure. 
Thus, when I look at a globe, which stands be. 
fore me, by the original powers of sight I per- 
ceive only something of a circular form, variously 
coloured. The visible figure hath no distance 
from the eye, no convexity, nor hath it three di- 
mensions ; even its length and breadth are in- 
capable of being measured by inches, feet, or 
other linear measures. But when I have learned 
to perceive the distance of every part of this ob- 
ject from the eye, this perception gives it con- 
vexity, and a spherical figure ; and adds a third 
dimension to that which had but two before. 
The distance of the whole object makes me like- 
wise perceive the real magnitude : for being accus- 
tomed to observe how an inch or a foot of length 
affects the eye at that distance, I plainly perceive 
by my eye the linear dimensions of the globe, 
and can affirm with certainty that its diameter is 
about one foot and three inches. 



SECT. 23.] OF SEEING. 343 

Tt was shewn in the seventh section of this 
chapter, that the visible figure of a body may, by 
mathematical reasoning, be inferred from its real 
figure, distance, and position, with regard to the 
eye : in like manner, we may, by mathematical 
reasoning, from the visible figure, together with 
the distance of the several parts of it from the 
eye, infer the real figure and position. But this 
last inference is not commonly made by mathe- 
matical reasoning, nor indeed by reasoning of 
any kind, but by custom. 

The original appearance which the colour of 
an object makes to the eye, is a sensation for 
which we have no name, because it is used mere- 
ly as a sign, and is never made an object of at- 
tention in common life : but this appearance 
according to the different circumstances, sig- 
nifies various things. If a piece of cloth of one 
uniform colour, is laid so that part of it is in the 
sun, and part in the shade ; the appearance of 
colour in these different parts, is very different : 
yet we perceive the colour to be the same ; we 
interpret the variety of appearance as a sign of 
light and shade, and not as a sign of real differ- 
ence in colour. ~But if the eye could be so far 
deceived, as not to perceive the difference of light 
in the two parts of the cloth, we should, in that 
case, interpret the variety of appearance to sig- 
nify a variety of colour in the parts of the cloth. 

Again, if we suppose a piece of cloth placed 
as before, but having the shaded part so much 
brighter in the colour, that it gives the same ap- 



344 OF THE HUMAN MIND, [CHAP. 6. 

pearance to the eye as the more enlightened part ; 
the sameness of appearance will here be inter- 
preted to signify a variety of colour, because we 
shall make allowance for the effect of light and 
shade. 

When the real colour of an object is known, 
the appearance of it indicates, in some circum- 
stances, the degree of light or shade ; in others, 
the colour of the circumambient bodies, whose 
rays are reflected by it ; and in other circum- 
stances, it indicates the distance or promixity of 
the object, as was observed in the last section ; 
and by means of these many other things are sug- 
gested to the mind. Thus, an unusual appear- 
ance in the colour of familiar objects may be the 
diagnostic of a disease in the spectator. The ap- 
pearance of things in my room, may indicate sun- 
shine or cloudy weather, the earth covered with 
snow, or blackened with rain. It hath been observ- 
ed, that the colour of the sky, in a piece of paint- 
ing, may indicate the country of the painter, be- 
cause the Italian sky is really of a different colour 
from the Flemish. 

It was already observed, that the original and 
acquired perceptions which we have by our 
senses, are the language of nature to man, which, 
in many respects, hath a great affinity to human* 
languages. The instances which we have given 
of acquired perceptions, suggest this affinity, that 
as, in human languages, ambiguities are often 
found, so this language of nature in our acquired 
perceptions is not exempted from them. We 



SECT. 23.] OF SEEING. 345 

have seen, in vision particularly, that the same 
appearance to the eye, may, in different circum- 
stances, indicate different things. Therefore, 
when the circumstances are unknown upon which 
the interpretation of the signs depends, their 
meaning must be ambiguous ; and when the cir- 
cumstances are mistaken, the meaning of the signs 
must also be mistaken. 

This is the case in all the phenomena which 
we call fallacies of the senses; and particularly, in 
those which are called fallacies in vision. The 
appearance of things to the eye always corre- 
sponds to the fixed laws of nature; therefore, if 
we speak properly, there is no fallacy in the 
senses. Nature always speaketh the same lan- 
guage, and useth the same signs in the same cir- 
cumstances: but we sometimes mistake the mean- 
ing of the signs, either through ignorance of the 
laws of nature, or through ignorance of the cir- 
cumstances which attend the signs. 

To a man unacquainted with the principles of 
optics, almost every experiment that is made with 
the prism, with the magic lanthorn, with the tele- 
scope, with the microscope, seems to produce 
some fallacy in vision. Even the appearance of 
a common mirror, to one altogether unacquainted 
with the effects of it, would seem most remark- 
ably fallacious. For how can a man be more im* 
posed upon, than in seeing that before him which 
is really behind him ? How can he be more im- 
posed upon, than in being made to see himself 
several yards removed from himself? Yet chil- 



Sid OF THE HUMAN MIND. [CHAP. 6. 

dren even before they can speak their mother- 
tongue, learn not to be deceived by these appear- 
ances. These, as well as all the other surprising 
appearances produced by optical glasses, are a 
part of the visual language; and, to those who 
understand the laws of nature concerning light 
and colours, are in no wise fallacious, but have a 
distinct and true meaning. 



SECT. XXIV. 



Of the analogy hehveen perceptio?i and the credit we 
give to human testimony. 

The objects of human knowledge are innumera- 
ble, but the channels by which it is conveyed to 
the mind are few. Among these, the perception 
of external things by our senses, and the infor- 
mations which we receive upon human testimony, 
are not the least considerable : and so remarkable 
is the analogy between these two, and the analo- 
gy between the principles of the mind, which are 
subservient to the one, and those which are sub- 
servient to the other, that, without further a- 
pology, we shall consider them together. 

In the testimony of nature given by the senses, 
as well as in human testimony given by language, 
things are signified to us by signs ; and in one, 
as well as the other, the mind, either by original 
principles, or by custom, passes from the sign to 



SECT. 23. J OF SEEING. 31<7 

the conception and belief of the things signifi- 
ed. 

We have distinguished our perceptions into 
original and acquired ; and language, into natu- 
ral and artificial. Between acquired perception, 
and artificial language, there is a great analogy ; 
but still a greater between original perception 
and natural language. 

The signs in original perception are sensations 
of which nature hath given us a great variety, 
suited to the variety of the things signified by 
them. Nature hath established a real connection 
between the signs and the things signified ; and 
Nature hath also taught us the interpretation of 
the signs ; so that, previous to experience, the 
sign suggests the thing signified, and creates the 
belief of it. 

The signs in natural language are features of 
the face, gestures of the body, and modulations 
of the voice; the variety of which is suited to 
the variety of the things signified by them. Na- 
ture hath established a real connection between 
these signs, and the thoughts and dispositions of 
the mind which are signified by them ; and na- 
ture hath taught us the interpretation of these 
signs ; so that, previous to experience, the signs 
suggest the thing signified, and create the belief 
of it. 

A man in company, without doing good or evil, 
without uttering an articulate sound, may behave 
himself gracefully, civilly, politely ; or, on the 
contrary, meanly, rudely and impertinently, 



818 OF THE HUMAN MIND. [CHAP. 6. 

We see the dispositions of his mind, by their na- 
tural signs in his countenance and behavour in 
the same manner as we perceive the figure and 
other qualities of bodies by the sensations which 
nature hath connected with them. 

The signs in the natural language in the human 
countenance and behaviour, as well as the signs 
in our original perceptions, have the same signi- 
fication in all climates, and in all nations; and 
the skill of interpreting them is not acquired, but 
innate. 

In acquired perception, the signs are either 
sensations, or things which we perceive by means 
of sensations. The connection between the sign 
and the thing signified, is established by nature : 
and we discover this connection by experience ; 
but not without the aid of our original percep- 
tions, or of those which we have already acquir- 
ed. After this connection is discovered, the 
sign, in like manner as in original perception, al- 
ways suggests the thing signified, and creates the 
belief of it. 

In artificial language, the signs are articulate 
sounds, whose connection with the things signi- 
fied by them is established by the will of men ; 
and in learning our mother tongue, we discover 
this connection by experience ; but not without 
the aid of natural language, or of what we had 
before attained of artificial language. And after 
this connection is discovered, the sign, as in na- 
tural language, always suggests the thing signi- 
ed, and creates the belief of it. 



SECT. 24.] OF SEEING. 349 

Our original perceptions are few, compared 
with the acquired; but without the former, we 
could not possibly attain the latter. In like man- 
ner, natural language is scanty, compared with 
artificial ; but without the former, we could not 
possibly attain the latter. 

Our original perceptions, as well as the natural 
language of human features and gestures, must 
be resolved into particular principles of the hu- 
man constitution. Thus, it is by one particular 
principle of our constitution, that certain features 
express anger ; and by another particular princi- 
ple, that certain features express benevolence. — 
It is in like manner, by one particular principle of 
our constitution, that a certain sensation signifies 
hardness in the body which I handle ; and it is by 
another particular principle, that a certain sensa- 
tion signifies motion in that body. 

But our acquired perceptions, and the infor- 
mation we receive by means of artificial language 
must be resolved into general principles of the 
human constitution. When a painter perceives 
that this picture is the work of Raphael, that the 
work of Titian ; a jeweller, that this is a true dia- 
mond, that a counterfeit ; a sailor, that this is 
a ship of five hundred tons, that of four hundred : 
these different acquired perceptions are produced 
by the same general principles of the human 
mind, which have a different operation in the 
same person, according as they are variously ap- 
plied, and in different persons according to the 
diversity of their education and manner of life. 



350 OF THE HUMAN MIND. [CHAP. 6- 

In like manner, when certain articulate sounds 
convey to my mind the knowledge of the battle 
of Pharsalia, and others, the knowledge of the 
battle of Pultowa ; when a Frenchman and an 
Englishman receive the same information by dif- 
ferent articulate sounds ; the signs used in these 
different cases produce the knowledge and belief 
of the thing signified, by means of the same ge- 
neral principles of the human constitution. 

Now, if we compare the general principles of 
our constitution which fit us for receiving infor- 
mation from our fellow-creatures by language, 
with the general principles which fit us for ac- 
quiring the perception of things by our senses, 
we shall find them to be very similar in their na- 
ture and manner of operation. 

When we begin to learn our mother-tongue, 
we perceive by the help of natural language, that 
they who speak to us, use certain sounds to ex- 
press certain things ; we imitate the same sounds 
when we would express the same things, and find 
that we are understood. 

But here a difficulty occurs which merits our 
attention, because the solution of it leads to some 
original principles of the human mind, which are 
of great importance, and of very extensive influ- 
ence. We know by experience that men have 
used such words to express such things. But all 
experience is of the past, and can, of itself, give 
no notion or belief of what is future* How come 
we then to believe and to rely upon it with assur- 
ance, that men who have it in their power to do 



SECT. 24.] OF SEEING. 351 

otherwise, will continue to use the same words 
when they think the same things? Whence comes 
this knowledge and belief, this foresight we ought 
rather to call it, of the future and voluntary ac- 
tions of our fellow creatures? Have they promis- 
ed that they will never impose upon us by equi- 
vocation or falsehood ? No, they have not. And, 
if they had, this would not solve the difficulty ; 
for such promise must be expressed by words, or 
by other signs ; and, before we can rely upon it, 
we must be assured, that they put the usual mean- 
ing upon the signs which express that promise. 
No man of common sense ever thought of taking- 
a man's own word for his honesty ; and it is evi- 
dent that we take his veracity for granted, when 
we lay any stress upon his word or promise. I 
might add, that this reliance upon the declara- 
tions and testimony of men is found in children 
long before they know what a promise is. 

There is, therefore, in the human mind an 
early anticipation, neither derived from experi- 
ence, nor from reason, nor from any compact or 
promise, that our fellow-creatures will use the 
same signs in language when they have the same 
sentiments. 

This is, in reality, a kind of prescience of hu- 
man actions ; and it seems to me to be an origi- 
nal principle of the human constitution, without 
which it would be incapable of language, and 
consequently incapable of instruction. 

The wise and beneficent Author of nature, 
who intended that we should be social creatures, 



35% OF THE HUMAN MIND. [CHAP. 6. 

and that we should receive the greatest and most 
important part of our knowledge by the informa- 
tion of others, hath, for these purposes, implant- 
ed in our natures, two principles that tally with 
each other. 

The first of these principles is, a propensity to 
speak truth, and to use the signs of language, so 
as to convey our real sentiments. This principle 
has a powerful operation, even in the greatest 
liars ; for, where they lie once, they speak truth 
a hundred times. Truth is always uppermost, 
and is the natural issue of the mind. It requires 
no art or training, no inducement or temptation, 
but only that we yield to a natural impulse. — 
Lying, on the contrary, is doing violence to our 
nature ; and is never practised, even by the 
worst men, without some temptation. Speaking 
truth is like using our natural food, which we 
would do from appetite, although it answered no 
end ; but lying is like taking physic, which is 
nauseous to the taste, and which no man takes 
but for some end which he cannot otherwise at- 
tain. 

If it should be objected, That men may be in- 
fluenced by moral or political considerations to 
speak truth, and therefore, that their doing so, 
is no proof of such an original principle as we 
have mentioned : I answer, first, That moral or 
political considerations can have no influence, 
until we arrive at years of understanding and re- 
flection : and it is certain from experience that 
children keep to truth invariably, before they are 



SECT. 24.] OF SEEING. 853 

capable of being influenced by such considera- 
tions. Secondly, When we are influenced by 
moral or political considerations, we must be con- 
scious of that influence, and capable of perceiv- 
ing it upon reflection. Now, when I reflect upon 
my actions most attentively, 1 am not conscious, 
that, in speaking truth, I am influenced on ordi- 
nary occasions by any motive moral or political. 
I find, that truth is always at the door of my lips, 
and goes forth spontaneously, if not held back. 
It requires neither good nor bad intention to 
bring it forth, but only that I be artless and un- 
designing. There may, indeed, be tempations 
to falsehood, which would be too strong for the 
natural principle of veracity, unaided by prin- 
ciples of honour or virtue ; but where there is no 
such temptation, we speak truth by instinct ; and 
this instinct is the principle I have been explain- 
ing. 

By this instinct, a real connection is formed 
between our words and our thoughts, and there- 
by the former become fit to be signs of the latter, 
which they could not otherwise be. And al- 
though this connection is broken in every instance, 
of lying and equivocation, yet these instances 
being comparatively few, the authority of human 
testimony is only weakened by them, but not 
destroyed. 

Another original priuciple implanted in us by 
the Supreme Being, is a disposition to confide in 
the veracity of others, and to believe what they 

z 



354* OF THE HUMAN MIND. [CHAP. 6. 

tell us. This is the counter-part to the former ; 
and as that may be called the principle of veracity, 
we shall, for want of a more proper name, call 
this the principle of credulity. It is unlimited in. 
children, until they meet with instances of deceit 
and falsehood : and it retains a very considerable 
degree of strength through life. 

If nature had left the mind of the speaker in 
cequilibriO) without any inclination to the side of 
truth more than to that of falsehood ; children 
would lie as often as they speak truth, until rea- 
son was so far ripened, as to suggest the impru- 
dence of lying, or conscience, as to suggest its 
immorality. And, if nature had left the mind of 
the hearer hi ceqiiilibrio, without any inclination 
to the side of belief more than to that of disbe- 
lief, we should take no man's word until we had 
positive evidence that he spoke truth. His tes- 
timony would, in this case, have no more autho- 
rity than his dreams ; which may be true or false, 
but no man is disposed to believe them, on this 
account, that they were dreamed. It is evident, 
that, in the matter of testimony, the balance of 
human judgment is by nature inclined to the side 
of belief; and turns to that side of itself, when 
there is nothing put into the opposite scale. If 
it was not so, no proposition that is uttered in dis- 
course would be believed, until it was examined 
and tried by reason ; and most men would be un- 
able to find reasons for believing the thousandth 
part of what is told them. Such distrust and in- 



SECT. 23. J OF SEEING, 355 

credulity would deprive us of the greatest bene- 
fits of society, and place us in a worse condition 
than that of savages. 

Children, on this supposition, would be abso- 
lutely incredulous ; and therefore absolutely in- 
capable of instruction: those who had little know- 
ledge of human life, and of the manners and 
characters of men, would be in the next degree 
incredulous; and the most credulous men would be 
those of greatest experience, and of the greatest 
penetration ; because, in many cases, they would 
be able to find good reasons for believing testi- 
mony, which the weak and the ignorant could 
not discover. 

In a word, if credulity were the effect of rea- 
soning and experience, it must grow up and ga- 
ther strength, in the same proportion as reason 
and experience do. But, if it is the gift of na- 
ture, it will be strongest in childhood, and limit- 
ed and restrained by experience j and the most 
superficial view of human life shews, that the 
last is realy the case, not the* first. 

It is the intention of nature, that we should 
be carried in arms before we are able to walk 
upon our legs ; and it is likewise the intention of 
nature, that our belief should be guided by the 
authority and reason of others, before it can be 
guided by our own reason. The weakness of the 
infant, and the natural affection of the mother, 
plainly indicate the former ; and the natural cre- 
dulity of youth, and authority of age, as plainly 

z2 



356 OF THE HUMAN MIND. [CHAP. 6. 

indicate the latter, The infant, by proper nurs- 
ing and care, acquires strength to walk without 
support. Reason hath likewise her infancy, 
when she must be carried in arms : when she 
leans entirely upon authority, by natural instinct, 
as if she was conscious of her own weakness ; and 
without this support, she becomes vertiginous. 
When brought to maturity by proper culture, 
she begins to feel her own strength, and leans 
less upon the reason of others - 9 she learns to sus- 
pect testimony in some cases, and to disbelieve 
it in others ; and sets bounds to that authority to 
which she was at first entirely subject. But still, 
to the end of life, she finds a necessity of borrow- 
ing light from testimony, where she has none 
within herself, and of leaning in some degree up- 
on the reason of others, where she is conscious of 
her own imbecility. 

And as in many instances, Reason, even in her 
maturity, borrows aid from testimony ; so in- 
others she mutually gives aid to it, and strengthens 
its authority. For as we find good reason to re- 
ject testimony in some cases, so in others we find 
good reason to rely upon it with perfect security, 
in our most important concerns. The character, 
the number, and the disinterestedness of witnesses, 
the impossibility of collusion, and the incredibili- 
ty of their concurring in their testimony without 
collusion, may give an irresistible strength ts> 
testimony, compared to which its native and in- 
trinsie authority is very inconsiderable. 



SECT. 24.] OF SEEING. 357 

Having now considered the general principles 
of the human mind which fit us for receiving in- 
formation from our fellow-creatures, by the means 
of language ; let us next consider the general 
principles which fit us for receiving the informa- 
tion of nature by our acquired perceptions. 

It is undeniable, and indeed is acknowledged 
by all, that when we have found two things to 
have been constantly conjoined in the course of 
nature, the appearance of one of them is imme- 
diately followed by the conception and belief of 
the other. The former becomes a natural sign 
of the latter ; and the knowledge of their con- 
stant conjunction in time past, whether got by 
experience or otherwise, is sufficient to make us 
rely with assurance upon the continuance of that 
conjunction. 

This process of the human mind is so famu 
liar, that we never think of inquiring into the 
principles upon which it is founded. We are 
apt to conceive it as a self-evident truth, that 
what is to come must be similar to what is 
past. Thus, if a certain degree of cold freezes 
water to-day, and has been known to do so in 
all time past, we have no doubt but the same 
degree of cold will freeze water to-morrow, or 
a year hence. That this is a truth which all 
men believe as soon as they understand it, I 
readily admit j but the question is, Whence does 
its evidence arise? Not from comparing the 
ideas, surely. For when I compare the idea of 



S5S OF THE HUMAN MIND. [CHAP. 6. 

cold with that of water hardened into a transpa- 
rent solid body, I can perceive no connection 
between them ; no man can show the one to be 
the necessary effect of the other ; no man can 
give a shadow of reason why nature hath conjoin- 
ed them. But do we not learn their conjunction 
from experience? True; experience informs us 
that they have been conjoined in time past; but 
no man ever had any experience of what is fu- 
ture; and this is the very question to be resolved, 
How we come to believe that the future will be 
like the past? Hath the Author of Nature pro- 
mised this ? Or were we admitted to his council 
when he established the present laws of nature, 
and determined the time of their continuance ? 
No, surely. Indeed, if we believe that there is a 
wise and good Author of Nature, we may see a 
good reason why he should continue the same 
laws of nature, and the same connections of 
things, for a long time: because, if he did other- 
wise, we could learn nothing from what is past, 
and all our experience would be of no use to us. 
But though this consideration, when we come to 
the use of reason, may confirm our belief of the 
continuance of the present course of nature, it 
is certain that it did not give rise to this belief; 
for children and idiots have this belief as soon as 
they know that fire will burn them. It must 
therefore be the effect of instinct, not of reason. 

The wise Author of our nature intended, that 
a great and necessary part of our knowledge 



SECT. 24.] OF SEEING. 359 

should be derived from experience, before we are 
capable of reasoning, and he hath provided meanfc 
perfectly adequate to this intention. For, first, 
He governs nature by fixed laws, so that we find 
innumerable connections of things which conti- 
nue from age to age. Without this stability of 
the course of nature, there could be no expe- 
rience ; or, it would be a false guide, and lead 
us into error and mischief. If there were not a 
principle of veracity in the human mind, men's 
words would not be signs of their thoughts : and 
if there were no regularity in the course of nature, 
no one thing could be a natural sign of another. 
Secondly, He hath implanted in human minds 
an original principle by which we believe and 
expect the continuance of the course of nature, 
and the continuance of those connections which 
we have observed in time past. It is by this ge- 
neral principle of our nature, that when two things 
have been found connected in time past, the ap- 
pearance of the one produces the belief of the 
other. 

I think the ingenious author of the Treatise of 
Human Nature first observed, that our belief of 
the continuance of the laws of nature cannot be 
founded either upon knowledge or probability : 
but, far from conceiving it to be an original prin- 
ciple of the mind, he endeavours to account for 
it from his favourite hypothesis, That belief is 
nothing but a certain degree of vivacity in the 
idea of the thing believed. I made a remark 



360 OF THE HUMAN MIND. [CHAP. 6* 

upon this curious hypothesis in the second chap- 
ter, and shall now make another. 

The belief which we have in perception, is a 
belief of the present existence of the object; that 
which we have in memory, is a belief of its past 
existence ; the belief of which we are now speak- 
ing, is a belief of its future existence, and in 
imagination there is no belief at all. Now, I 
would gladly know of this author, how one de- 
gree of vivacity fixes the existence of the object 
to the present moment ; another carries it back 
to time past; a third, taking a contrary direqtion, 
carries it into futurity; and a fourth carries it 
out of existence altogether. Suppose, for in- 
stance, that I see the sun rising out of* the sea ; 
I remember to have seen him rise yesterday; I 
believe he will rise to-morrow near the same 
place ; I can likewise imagine him rising in that 
place without any belief at all. Now, according 
to this sceptical hypothesis, this perception, this 
memory, this foreknowledge, and this imagina- 
tion, are all the same idea, diversified only by 
different degrees of vivacity. The perception of 
the sun rising, is the most lively idea ; the me- 
mory of his rising yesterday, is the same idea, a 
little more faint ; the belief of his rising to-mor- 
row, is the same idea yet fainter ; and the ima- 
gination of his rising, is still the same idea, but 
faintest of all. One is apt to think, that this idea 
might gradually pass through all possible degrees 
of vivacity, without stirring out of its place. But 



SECT. 24.] OF SEEING. 36 1 

if we think so, we deceive ourselves ; for no 
sooner does it begin to grow languid, than it 
moves backward into time past. Supposing this 
to be granted, we expect at least that as it moves 
backward by the decay of its vivacity, the more 
that vivacity decays, it will go back the farther, 
until it remove quite out of sight. But here we 
are deceived again : for there is a certain period 
of this declining vivacity, when, as if it had met 
an elastic obstacle in its motion backward, it sud- 
denly rebounds from the past to the future, with- 
out taking the present in its way. And now 
having got into the regions of futurity, we are 
apt to think, that it has room enough to spend all 
its remaining vigour : but still we are deceived ; 
for by another sprightly bound, it mounts up in- 
to the airy region of imagination. So that ideas, 
in the gradual declension of their vivacity, seem 
to imitate the inflection of verbs in grammar. — 
They begin with the present, and proceed in or- 
der to the preterite, the future, and the indefinite. 
This article of the sceptical creed is indeed so full 
of mystery, on whatever side we view it, that they 
who hold that creed are very injuriously charged 
with incredulity: for to me it appears to require 
as much faith as that of St. Athanasius. 

However, we agree with the author of the 
Treatise of Human Nature in this, That our be- 
lief of the continuance of nature's laws is not de- 
rived from reason. It is an instinctive prescience 
of the operations of nature, very like to that pre- 



362 OF THE HUMAN MIND. [CHAP. 6. 

science of human actions which makes us rely 
upon the testimony of our fellow- creatures ; and 
as, without the latter, we should be incapable of 
receiving information from men by language ; so, 
without the former, we should be incapable of re- 
ceiving the information of nature by means of ex- 
perience. 

All our knowledge of nature beyond our ori- 
ginal perceptions, is got by experience, and con- 
sists in the interpretation of natural signs. The 
constancy of nature's laws connects the sign with 
the thing signified, and, by the natural principle 
just now explained, we rely upon the continuance 
of the connections which experience hath discover- 
ed; and thus the appearance of the sign, is fol- 
lowed by the belief of the thing signified. 

Upon this principle of our constitution, not 
only acquired perception, but all inductive rea- 
soning, and all our reasoning from analogy, is 
grounded : and therefore for want of another 
name, we shall beg leave to call it the inductive 
principle. It is from the force of this principle, 
that we immediately assent to that axiom upon 
which all our knowledge of nature is built. That 
effects of the same kind must have the same 
cause. For effects and causes, in the operations 
of nature, mean nothing but signs, and the things 
signified by them. We perceive no proper casu- 
alty, or efficiency in any natural cause; but. on- 
ly a connection established by the course of na- 
ture between it and what is called its effect. An- 



SECT. 24.] OP SEEING. 363 

tecedently to all reason ing 9 we have by our con- 
stitution, an anticipation, that there is a fixed and 
steady course of nature : and we have an eager 
desire to discover this course of nature. We at- 
tend to every conjunction of things which pre- 
sents itself, and expect the continuance of that 
conjunction. And when such a conjunction has 
been often observed, we conceive the things to 
be naturally connected, and the appearance of 
one without any reasoning or reflection, carries 
along with it the belief of the other. 

If any reader should imagine that the induc- 
tive principle may be resolved into what philo- 
sophers usually call the association of ideas, let 
him observe, that, by this principle, natural signs 
are not associated with the idea only, but with 
the belief of the things signified. Now, this can 
with no propriety be called an association of 
ideas, unless ideas and belief be one and the same 
thing. A child has found the prick of a pin 
conjoined with pain ; hence he believes, and 
he knows that the one will always follow the 
other. If any man will call this only an association 
of ideas, I dispute not about words, but I think 
he speaks very improbably. For if we express it 
in plain English, it is a prescience, that tilings 
which he hath found conjoined in time past, will 
be conjoined in time to come. And this presci- 
ence is not the effect of reasoning, but of an ori. 
ginal principle of human nature, which 1 have 
called the inductive principle. 



S64f OF THE HUMAN MIND. [CHAP. 6. 

This principle, like that of credulity, is unlimit- 
ed in infancy, and gradually restrained and regu- 
lated as we grow up. It leads us often into mis- 
takes, but is of infinite advantage upon the whole. 
By it the child once burnt shuns the fire ; by it, 
he likewise runs away from the surgeon by whom 
he was inoculated. It is better that he should 
do the last, than that he should not do the first. 

But the mistakes we are led into by these two 
natural principles are of a different kind. Men 
sometimes lead us into mistakes, when we per- 
fectly understand their language, by speaking 
lies. But nature never misleads us in this way ; 
her language is always true ; and it is only by 
misinterpreting it that we fall into error. There 
must be many accidental conjunctions of things, 
as well as natural connections ; and the former 
are apt to be mistaken for the latter. Thus, in 
the instance above mentioned, the child connect- 
ed the pain of inoculation with the surgeon ; 
whereas it was really connected with the incision 
only. Philosophers, and men of science, are not 
exempted from such mistakes ; indeed all false 
reasoning in philosophy is owing to them : it is 
drawn from experience and analogy, as well 
as just reasoning, otherwise it could have no 
verisimilitude : but the one is an unskilful and 
rash, the other a just and legitimate, interpreta- 
tion of natural signs. If a child, or a man of 
common understanding, were put to interpret a 
book of science wrote in his mother tongue, how 
many blunders and mistakes would he be apt to 



SECT. 24.] OF SEEING. 365 

fall into? Yet be knows as much of this language 
as is necessary for his manner of life. 

The language of nature is the universal study ; 
and the students are of different classes. Brutes, 
idiots, and children, employ themselves in this 
study, and owe to it all their acquired perceptions. 
Men of common understanding make a greater 
progress, and learn, by a small degree of reflec- 
tion, many things of which children are igno- 
rant. 

Philosophers fill up the highest form in this 
school, and are critics in the language of nature. 
All these different classes have one teacher, Ex- 
perience, enlightened by the inductive principle. 
Take away the light of this inductive principle, 
and Experience is as blind as a mole : she may 
indeed feel what is present, and what immediate- 
ly touches her : but she sees nothing that is either 
before or behind, upon the right hand or upon the 
left, future or past. 

The rules of inductive reasoning, or of a just 
interpretation of nature, as well as the fallacies 
by which we are apt to misinterpret her language, 
have been, with wonderful sagacity, delineated 
by the great genius of Lord Bacon : so that his 
JSovum organum may justly be called a grammar 
of the language of nature. It adds greatly to the 
merit of this work, and atones for its defects, 
that at the time it was written, the world had not 
seen any tolerable model of inductive reasoning, 
from which the rules of it might be copied. The 



366 OF THE HUMAN MIND. [CHAP. 6. 

arts of poetry and eloquence were grown up to 
perfection when Aristotle described them ; but 
the art of interpreting nature was yet in embryo 
when Bacon delineated its manly features and 
proportions. Aristotle drew his rules from the 
best models of those arts that have yet appeared ; 
but the best models of inductive reasoning that 
have yet appeared, which I take to be the third 
book of the Principia and the Optics of Newton, 
were drawn from Bacon's rules. The purpose of 
all those rules, is to teach us to distinguish seem- 
ing or apparent connections of things in the course 
of nature, from such as are real. 

They that are unskilful in inductive reasoning, 
are more apt to fall into error in their reasonings 
from the phenomena of nature than in their etc- 
quired perceptions ; because we often reason from 
a few instances, and thereby are apt to mistake 
accidental conjunctions of things for natural 
connections : but that habit of passing, without 
reasoning, from the sign to the things signified, 
which constitutes acquired perception, must be 
learned by many instances or experiments ; and 
the number of experiments serves to disjoin those 
things which have been accidentally conjoined, 
as well as to confirm our belief of natural con- 
nections. 

From the time Chat children begin to use their 
hands, nature directs them to handle every thing 
over and over, to look at it while they handle it, 
and to piit it into various positions, and at various 



StfCT. 21*.] OF SEEING. 36j 

distances from the eye. We are apt to excuse 
this as a childish diversion, because they must be 
doing something, and have not reason to enter- 
tain themselves in a more manly way. But if 
we think more justly, we shall find that they are 
engaged in the most serious and important study j 
and if they had all the reason of a philosopher, 
they could not be more properly employed. For 
it is this childish employment that enables them 
to make the proper use of their eyes. They are 
thereby every day acquiring habits of perception, 
which are of greater importance than any thing 
we can teach them. The original perceptions 
which nature gave them are few, and insufficient 
for the purposes of life ; and therefore she made 
them capable of acquiring many more percep- 
tions by habit. And to complete her work, she 
hath given them an unwearied assiduity in ap- 
plying to the exercises by which those percep- 
tions are acquired. 

This is the education which nature gives to 
her children. And since we have fallen upon 
this subject, we may add, that another part of 
nature's education is, That by the course of 
things, children must often exert all their mus- 
cular force, and employ all their ingenuity, in or- 
der to gratify their curiosity, and satisfy their 
little appetites. What they desire is only to be 
obtained at the expence of labour and patience, 
and many disappointments. By the exercise of 
body and mind necessary for satisfying their de- 



368 OF THE HUMAN MIND, [CHAP. 6. 

sires, they acquire agility, strength, and dexterity 
in their motions, as well as health and vigour to 
their constitutions : they learn patience and per- 
severance ; they learn to bear pain without de- 
jection, and disappointment without despondence. 
The education of nature is most perfect in sa- 
vages, who have no other tutor; and we see, that, 
in the quickness of all their senses, in the agility 
of their motions, in the hardiness of their consti- 
tutions, and in the strength of their minds to 
bear hunger, thirst, pain, and disappointment, 
they commonly far exceed the civilized. A 
most ingenious writer on this account, seems to 
prefer the savage life to that of society. But 
the education of nature could never of itself 
produce a Rousseau. It is the intention of na- 
ture, that human education should be joined to 
her institution, in order to form the man. And she 
hath fitted us for human education, by the natural 
principles of imitation and credulity, which dis- 
cover themselves almost in infancy, as well as by 
others which are of later growth. 

When the education which we receive from 
men does not give scope to the education of na- 
ture, it is wrong directed ; it tends to hurt our 
faculties of perception, and to enervate both the 
body and mind. Nature hath her way of rearing 
men, as she hath of curing their diseases. The 
art of medicine is to follow nature, to imitate and 
to assist her in the cure of diseases ; and the art 
of education is to follow Nature, to assist and to 



SECT. 24.] OF SEEING. 3C9 

imitate her in her way of rearing men. The an- 
cient inhabitants of the Baleares followed nature 
in [ the manner of teaching their children to be 
good archers, when they hung their dinner aloft 
by a thread, and left the younkers to bring it 
down by their skill in archery. 

The education of nature, without any more 
human care than is necessary to preserve life, 
makes a perfect savage. Human education, join- 
ed to that of nature, may make a good citizen, 
a skilful artisan, or a well-bred man. But Reason 
and Reflection must superadd their tutory, in 
order to produce a Rousseau, a Bacon, or a 
Newton. 

Notwithstanding the innumerable errors com- 
mitted in human education, there is hardly any 
education so bad, as to be worse than none. — 
And I apprehend, that if even Rousseau were to 
choose whether to educate a son among the 
French, the Italians, the Chinese, or among the 
Eskimaux, he would not give the preference to 
the last. 

When reason is properly employed, she will 
confirm the documents of nature, which are al- 
ways true and wholesome ; she will distinguish, 
in the documents of human education, the good 
from the bad, rejecting the last with modesty, 
and adhering to the first with reverence. 

Most men continue all their days to be just 
what nature and human education made them. — 
Their manners, their opinions, their virtues, and 

2 v 



370 OF THE HUMAN MIND, [CHAP. 6, 

their vices, are all got by habit, imitation, and 
instruction ; and Reason has little or no share in 
forming them. 



CHAP. 7.] CONCU*fON. 371 



CHAR VII. 



CONCLUSION. 



Containing Reflections upon the opinions of Vhilo* 
sopliers on this subject. 

There are two ways in which men may form 
their notions and opinions concerning the mind, 
and concerning its powers and operations. The 
first is the only way that leads to truth ; but it is 
narrow and rugged, and few have entered upon 
it. The second is broad and smooth, and hath 
been much beaten, not only by the vulgar, but 
even by philosophers : it is sufficient for common 
life, and is well adapted to the purposes of the 
poet and orator : but, in philosophical disquisi- 
tions concerning the mind, it leads to error and 
delusion. 

We may call the first of these ways, the "way of 
reflection. When the operations of the mind are 
exerted, we are conscious of them ; and it is in 
our power to attend to them, and to reflect up- 
on them, until they become familiar objects of 
thought. 

This is the only wav in which we can form 

n2 



572 OF THE HUMAN MIN0. [CHAP, 7* 

just and accurate notions of those operations. 
But this attention and reflection is so difficult to 
man, surrounded on all hands fey external objects 
which constantly solicit his attention, that it has 
been very little practised, even by philosophers. 
In the course of this Inquiry, we have had many 
occasions to show, how little attention Inth been 
given to the most familiar operations of the 
senses. 

The second, and the most common way, ir* 
which men form their opinions concerning the 
mind and its operations, we may call the way of 
analogy. There is nothing in tjie course of na- 
ture so singular, but we can find some resem- 
blance, or at least some analogy, between it and 
other things with which we are acquainted. The 
mind naturally delights in hunting after such 
analogies, and attends to them with pleasure. 
From them, poetry and wit derive a great part of 
their charms; and eloquence, not a little of its 
persuasive force. 

Besides the pleasure we receive from analogies, 
they are of very considerable use, both to facili- 
tate the conception of things, when they are not 
easily apprehended without such a handle, and 
to lead us to probable conjectures about their 
nature and qualities, when we want the means of 
more direct and immediate knowledge. When 
I consider that the planet Jupiter, in like manner 
as the earth, rolls round his own axis, and revolves 
round the sun, and that he is enlightened by se« 



CHAP. 7.] CONCLUSION. 373 

veral secondary planets, as the earth is enlight- 
ened by the moon ; 1 am apt to conjecture from 
analogy, that as the earth by these means is fitted 
to be the habitation of various orders of animals, 
so the planet Jupiter is, by the like means, fitted 
for the same purpose : and having no argument 
more direct and conclusive to determine me in 
this point, I yield to this analogical reasoning, a 
degree of assent proportioned to its strength. — 
When I observe, that the potato plant very much 
resembles the solarium in its flower and fructifica- 
tion, and am informed that the last is poisonous, 
I am apt from analogy to have some suspicion of 
the former : but in this case I have access to more 
direct and certain evidence ; and therefore ought 
not to trust to analogy, which would lead me in- 
to an error. 

Arguments from analogy are always at hand, 
and grow up spontaneously in a fruitful imagina- 
tion, while arguments that are more direct, and 
more conclusive, often require painful attention 
and application : and therefore mankind in gene- 
ral have been very mucli disposed to trust to the 
former. If one attentively examines the systems 
of the ancient philosophers, either concerning 
the material world, or concerning the mind, he 
will find them to be built solely upon the found- 
ation of analogy. Lord Bacon first delineated 
the strict and severe method of induction ; since 
his time it has been applied with very happy suc- 
cess in some parts of natural philosophy j and 



374» OF THE HUMAN MIND. [CHAP. 7. 

hardly in any thing else. But there is no subject 
in which mankind are so much disposed to trust 
to the analogical way of thinking and reasoning 
as in what concerns the mind and its operations ; 
because to form clear and distinct notions of those 
operations in the direct and proper way, and to 
reason about them, requires a habit of attentive 
reflection, of which few are capable, and which, 
even by those few, cannot be attained without 
much pains and labour. 

Every man is apt to form his notions of things 
difficult to be apprehended, or less familiar, from 
their analogy to things which are more familiar. 
Thus, if a man bred to the seafaring life, and ac- 
customed to think and talk only of matters relat- 
ing to navigation, enters into discourse upon any 
other subject, it is well known that the language 
and the notions proper to his own profession are 
infused into every subject, and all things are mea- 
sured by the rules of navigation : and if he should 
take it into his head to philosophize concerning 
the faculties of the mind, it cannot be doubted, 
but he would draw his notions from the fabric of 
his ship, and would find in the mind, sails, masts, 
rudder, and compass. 

Sensible objects of one kind or other, do no 
less occupy and engross the rest of mankind, than 
things relating to navigation, the sea-faring man. 
For a considerable part of life, we can think of 
nothing but the objects of sense; and to attend 
to objects of another nature, so as to form clear 



CHAP. 7«] CONCLUSION. 375 

and distinct notions of them, is no easy matter, 
even after we come to years of reflection. The 
condition of mankind, therefore, affords good rea- 
son to apprehend, that their language, and their 
common notions, concerning the mind and its 
operations, will be analogical, and derived from 
the objects of sense ; and that these analogies 
will be apt to impose upon philosophers, as well 
as upon the vulgar, and to lead them to material- 
ize the mind and its faculties ; and experience 
abundantly confirms the truth of this. 

How generally men of all nations, and in all 
ages of the world, have conceived the soul, or 
thinking principle in man, to be some subtile 
matter like breath or wind, the names given to 
it in almost all languages sufficiently testify. We 
have words which are proper, and not analogical, 
to express the various ways in which we perceive 
external objects by the senses; such as feeling, 
sight, taste : but we are often obliged to use these 
words analogically, to express other powers of the 
mind which are of a very different nature. And 
the powers which imply some degree of reflec- 
tion, have generally no names but such as are 
analogical. The objects of thought are said to 
be in the mind, to be apprehended \ comprehended, 
conceived, imagined, retained, weighed, ruminated. 

It does not appear that the notions of the an- 
cient philosophers, with regard to the nature of 
the soul, were much more refined than those of the 
vulgar, or that they were formed in any other way. 



376 OF THE HUMAN MIND. [CHAP. 7» 

We shall distinguish the philosophy that regards 
our subject, into the old and the new. The old 
reached down to Des Cartes, who gave it a fatal 
blow, of which it has been gradually expiring ever 
since, and is now almost extinct. Des Cartes is 
the father of the new philosophy that relates to 
this subject; but it hath been gradually improving 
since his time, upon the principles laid down by 
him. The old philosophy seems to have been 
purely analogical : the new is more derived from 
reflection, but still with a very considerable mix- 
ture of the old analogical notions. 

Because the objects of sense consist of matter 
and Jorm, the ancient philosophers conceived 
every tiling to belong to one of these, or to be 
made up of both. Some therefore thought, that 
the soul is a particular kind of subtile matter, 
separable from our gross bodies; others thought 
that it is only a particular form of the body, and 
inseparable from it. For there seems to have been 
some among the ancients, as well as among the mo- 
derns, who conceived that a certain structure or 
organization of the body, is all that is necessary 
to render it sensible and intelligent. The differ- 
ent powers of the mind were, accordingly, by the 
last sect of philosophers, conceived to belong to 
different parts of the body, as the heart, the brain, 
the liver, the stomach, the blood. 

They who thought that the soul is a subtile 
matter, separable from the body, disputed to 
which of the four elements it belongs, whether 



CHAP. 7«] CONCLUSION. 377 

to earth, water, air, ot fire. Of the three last 
each had its particular advocates. But some 
were of opinion, that it partakes of all the 
elements ; that it must have something in its 
composition similar to every thing we perceive ; 
and that we perceive earth by the earthly part ; 
water, by the watery part ; and fire by the fiery 
part of the soul. Some philosophers, not satisfi- 
ed with determining of what kind of matter the 
soul is made, inquired likewise into its figure, 
which they determined to be spherical, that it 
might be the more fit for motion. The most 
spiritual and sublime notion concerning the na- 
ture of the soul to be met with among the ancient 
philosophers, I conceive to be that of the Plato- 
nists, who held, that it is made of that celestial 
and incorruptible matter' of which the fixed stars 
were made, and therefore has a natural tendency 
to rejoin its proper element. 1 am at a loss to 
say, in which of these classes of philosophers 
Aristotle ought to be placed*?. He defines the 
soul to be, The first m*|gfi* of a natural body 
which has potential life. I beg to be excused 
from translating the Greek word, because I know 
not the meaning of it. 

The notions of the ancient philosophers with 
regard to the operations of the mind, particularly 
with regard to perceptions and ideas, seem like- 
wise to have been formed by the same kind of 
analogy. 

Plato, of the writers that are extant, first in- 



378 OF THE HUMAS MIND. [CHAP. J. 

troduced the word idea into philosophy ; but his 
doctrine upon this subject had somewhat pecu- 
liar. He agreed with the rest of the ancient phi- 
losophers in this, that all things consist of matter 
and form ; and that thermtterof which all things 
were made, existed from eternity, without form ; 
but he likewise believed, that there are eternal 
forms of all possible things which exist, without 
matter; and to these eternal and immaterial forms 
he gave the name of ideas - y maintaining, that 
they are the only object of true knowledge. It is 
of no great moment to us, whether he borrowed 
these notions from Parmekides, or whether they 
were the issue of his own creative imagination. 
The latter Flatonists seem to have improved upon 
them, in conceiving those ideas, or eternal forms 
of things, to exist not of themselves, but in the 
Divine Mind, and to be the models and patterns 
according to which all things were made : 

Then lived the Eternal One, then, deep rctird 
In his nnfathoni'd essence, viewed at large 
The uncreated images of things. 

To these Platonic notions, that of Malebranche 
is very nearly allied. This author seems, more 
than any other, to have been aware of the diffi- 
culties attending the common hypothesis con- 
cerning ideas, to wit, That ideas of all objects of 
thought are in the human mind ; and therefore, 
in order to avoid those difficulties, makes the 
ideas which are the immediate objects of human 



CHAP. 7.] CONCLUSION. 379 

thought, to be the ideas of things in the Divine 
Mind ; who being intimately present to every hu- 
man mind, may discover his ideas to it, as far as 
pleaseth him. 

The Platonists and Malebranche excepted, all 
other philosophers, as far as I know, have con- 
ceived that there are ideas or images of every ob- 
ject of thought in the human mind, or at least in 
some part of the brain, where the mind is supposed 
to have its residence. 

Aristotle had no good affection to* the word 
idea, and seldom or never uses it but in refuting 
Plato's notions about ideas. He thought that 
matter may exist without form ; but that form 
cannot exist without matter. But at the same 
time he taught, That there can be no sensation, 
no imagination, nor intellection, without forms, 
phantasms, or species in the mind; and that 
things sensible are perceived by sensible species, 
and things intelligible by intelligible species. 
His followers taught more explicitly, that those 
sensible and intelligible species are sent forth by 
the objects, and make their impressions upon the 
passive intellect ; and that the active intellect 
perceives them in the passive intellect. And this 
seems to have been the common opinion while 
the Peripatetic philosophy retained its authority. 

The Epicurean doctrine, as explained by Lu- 
cretius, though widely different from the Peripa- 
tetic in many things, is almost the same in this. 
He affirms, that slender films or ghosts (tenuia 



330 OF THE HUMAN MIND. [ CHAP « 7* 

rerum simulacra) are still going off from all things 
and flying about ; and that these being extremely 
subtile, easily penetrate our gross bodies, and 
striking upon the mind, cause thought and ima- 
gination. 

After the Peripatetic system had reigned above 
a thousand years in the schools of Europe, almost 
without a rival, it sunk before that of Des Cartes; 
the perspicuity of whose writings and notions, 
contrasted with the obscurity of Aristotle and 
his commentators, created a strong prejudice in 
favour of this new philosophy. The character- 
istic of Plato's genius was sublimity, that of 
Aristotle subtilty ; but Des Cartes far excel- 
led both in perspicuity, and bequeathed this spirit 
to his successors. The system which is now ge- 
nerally received, with regard to the mind and its 
operations, derives not only its spirit from Des 
Cartes, but its fundamental principles ; and after 
all the improvements made by Malebranche, 
Locke, Berkeley, and Hume, may still be call- 
ed the Cartesian system: we shall therefore make 
some remarks upon its spirit and tendency in ge- 
neral, and upon its doctrine concerning ideas in 
particular. 

It may be observed, That the method which 
Des Cartes pursued, naturally led him to attend 
more to the operations of the mind by accurate 
reflection, and to trust less to analogical reason- 
ing upon this subject, than any philosopher had 
done before him. Intending to build a sys- 



CHAP. 7.] CONCLUSION. 381 

tern upon a new foundation, he began with a 
resolution lo admit nothing but what was abso- 
lutely certain and evident. He supposed that 
his senses, his memory, his reason, and every 
other faculty to which we trust in common life, 
might be fallacious - y and resolved to disbelieve 
every thing, until he was compelled by irresistible 
evidence to yield assent. 

In this method of proceeding, what appeared 
to him first of all certain and evident, was, That 
he thought, that he doubted, that he deliberated. 
In a word, the operations of his own mind, of 
which he was conscious, must be real, and no 
delusion ; and though all his other faculties should 
deceive him, his consciousness could not. This 
therefore he looked upon as the first of all truths. 
This was the first firm ground upon which he set 
his foot, after being tossed in the ocean of scep- 
ticism ; and he resolved to build all knowledge 
upon it, without seeking after any more first 
principles. 

As every other truth, therefore, and particu- 
larly the existence of the objects of sense, was 
to be deduced by a train of strict argumentation 
from what he knew by consciousness, he was na- 
turally led to give attention to the operations of 
which he was conscious, without borrowing his 
notions of them from external things. 

It was not in the way of analogy, but of at- 
tentive reflection, that he was led to observe, 
That thought, volition, remembrance, and the 



382 OF THE HUMAN MIND, [CHAP. 6a 

other attributes of the mind, are altogether un- 
like to extension, to figure, and to all the attri- 
butes of body; that we have no reason, there* 
fore, to conceive thinking substances to have any 
resemblance to extended substances; and that, 
as the attributes of the thinking substance are 
things of which we are conscious, we may have a 
more certain and immediate knowledge of them 
by reflection, than w r e can have of external ob- 
jects by our senses. 

These observations, as far as I know, were first 
made by Des Cartes ; and they are of more im- 
portance, and throw more light upon the subject, 
than all that had been said upon it before. They 
ought to make us diffident and jealous of every 
notion concerning the mind and its operations, 
which is drawn from sensible objects in the way of 
analogy, and to make us rely only upon accurate 
reflection, a? the source of all real knowledge 
upon this subject 

2. I observe, that as the Peripatetic system has 
a tendency to materialize the mind and its ope- 
rations ; so the Cartesian has a tendency to spi- 
ritualize body, and its qualities. One error, com- 
mon to both systems, leads to the first of these 
extremes in the way of analogy, and to the last, 
in the way of reflection. The error I mean is, 
That we can know nothing about body, or its 
qualities, but as far as we have sensations, which 
resemble those qualities. Both systems agreed 
in this: but according to their different methods 



chap. 7.] CONCLUSION. 363 

of reasoning, they drew yery different conclusions 
from it ; the Peripatetic drawing his notions of 
sensation from the qualities of body ; the Car- 
tesian, on the contrary, drawing his notions of the 
qualities of body from his sensations. 

The Peripatetic, taking it for granted that 
bodies and their qualities do really exist, and are 
such as we commonly take them to be, inferred 
from them the nature of his sensations, and rea- 
soned in this manner : Our sensations are the 
impressions which sensible objects make upon 
the mind, and may be compared to the impres- 
sion of a seal upon wax; the impression is the 
image or form of the seal, without the matter of 
it : in like manner, every sensation is the image 
or form of some sensible quality of the object. 
This is the reasoning of Aristotle, and it has 
an evident tendency to materialize the mind and 
its sensations. 

The Cartesian, on the contrary, thinks that 
the existence of body, or of any of its qualities, 
is not to be taken as a first principle : and that 
we ou£ht to admit nothing concerning it, but 
what, by just reasoning, can be deduced from our 
sensations ; and he knows that, by reflection, we 
can form clear and distinct notions of our sensa- 
tions, without borrowing our notions of them by 
analogy from the objects of sense. The Carte- 
sians, therefore, beginning to give attention to 
their sensations, first discovered that the sensa- 
tions corresponding to secondary qualities, can- 



384> OF THE HUMAN MIND. [CHAP. 7] 

not resemble any quality of body. Hence Des 
Cartes and Locke inferred, that sound, taste, 
smell, colour, heat, and cold, which the vulgar 
took to be qualities of body, were not qualities 
of body, but mere sensations of the mind. Af- 
terwards the ingenious Berkeley, considering 
more attentively the nature of sensation in gene- 
ral, discovered, and demonstrated, that no sensa- 
tion whatever could possibly resemble any quality 
of an insentient being, such as body is supposed 
to be: and hence he inferred, very justly, that 
there is the same reason to hold extension, figure, 
and all the primary qualities, to be mere sensa- 
tions, as there is to hold the secondary qualities 
to be mere sensations. Thus, by just reasoning 
upon the Cartesian principles, matter was stript 
of all its qualities ; the new system, by a kind of 
mataphysicat sublimation, converted all the qua- 
lities of matter into sensation, and spiritualized 
body, as the old had materialized spirit. 

The way to avoid both these extremes, is, to 
admit the existence of/what we see and feel as a 
first principle, as well as the existence of things 
whereof we are conscious; and to take our no- 
tions of the qualities of body, from the testimony 
of our senses, with the Peripatetics ; and our no- 
tions of our sensations, from the testimony of 
consciousness, with the Cartesians. 

3. I observe, That the modern scepticism is 
the natural issue of the new system ; and that, 
although it did not bring forth this monster un- 



CHAP. 70 CONCLUSION. 885 

til the year 1739, it may be said to have carried 
it in its womb from the beginning. 

The old system admitted all the principles of 
common sense as first principles, without requir- 
ing any proof of them; and therefore, though its 
reasoning was commonly vauge, analogical, and 
dark, yet it was built upon a broad foundation, 
and had no tendency to scepticism. We do not 
find that any Peripatetic thought it incumbent 
upon him to prove the existence of a material 
world; but every writer upon the Cartesian sys- 
tem attempted this, until Berkeley clearly de- 
monstrated the futility of their arguments; and 
thence concluded, that there was no such thing 
as a material world; and that the belief of it ought 
to be rejected as a vulgar error. 

The new system admits only one of the princi- 
ples of common sense as a first principle; and 
pretends, by strict argumentation, to deduce all 
the rest from it. That our thoughts, our sensa- 
tions, and every thing of which we are conscious, 
hath a real existence, is admitted in this system 
as a first principle; but every thing else must be 
made evident by the light of reason. Reason 
must rear the whole fabric of knowledge upon 
this single principle of consciousness. 

There is a disposition in human nature to re- 
duce things to as few principles as possible; and 
this, without doubt, adds to the beauty of a sys- 
tem, if the principles are able to support what 
rests upon them. The mathematicians glory, 



2 B 



386' OF THE HUMAN MIND. [CHAP. 7« 

very justly, in having raised so noble and magni- 
ficent a system of science, upon the foundation of 
a few axioms and definitions. The love of sim- 
plicity, of reducing things to few principles, hath 
produced many a false system; but there never 
was any system in which it appears so remarka- 
bly as that of Des Cartes. His whole system 
concerning matter and spirit is built upon one 
axiom, expressed in one word, Cogito. Upon 
the foundation of conscious thought, with ideas 
for his materials, he builds his system of the hu- 
man understanding, and attempts to account for 
all its phenomena: And having, as he imagined, 
from his consciousness, proved the existence of 
matter, and of a certain quality of motion origi- 
nally impressed upon it, he builds his system of 
the material world, and attempts to account for 
all its phenomena. 

These principles with regard to the material sys- 
tem have been found insufficient; and it has been 
made evident, that besides matter and motion, 
ive must admit gravitation, cohesion, corpuscular 
attraction, magnetism, and other centripetal and 
-centrifugal forces, by which the particles of 
matter attract and repel each other. Newton 
having discovered this, and demonstrated that 
these principles cannot be resolved into matter 
and motion, was led by analogy and the love of 
simplicity, to conjecture, but with a modesty and 
caution peculiar to him, that all the phenomena 
of the material world depended upon attracting 



CHAP. 3.] CONCLUSION. N s 387 

and repelling forces in the particles of matter. 
But we may now venture to say, that this conjec- 
ture fell short of the mark. For even in the unor- 
ganized kingdom, the powers by which salts, 
crystal, spars, and many other bodies, concrete 
into regular forms, can never be accounted for by 
attracting and repelling forces in the particles of 
matter. And in the vegetable and animal king- 
doms, there are strong indications of powers of a 
different nature from all the powers of unorganiz- 
ed bodies. We see then, that although in the 
structure of the material world there is, without 
doubt, all the beautiful simplicity consistent with 
the purposes for which it was made, it is not so 
simple as the great Des Cartes determined it to 
be: nay, it is not so simple as the greater New- 
ton modestly conjectured it to be. Both were 
misled by analogy, and the love of simplicity. 
One hath been much conversant about extension, 
figure, and motion; the other had enlarged his 
views to attracting and repelling forces ; and both 
formed their notions of the unknown parts of na- 
ture, from those with which they were acquaint- 
ed, as the shepherd Titrus formed his notion of 
the city of Rome from his country village : 

Urbem qxuarti dicunt Roman, Melibcee, putavi 
Stultus ego huic nostra: similem, quo sccpc solcmus 
Pastores ovium teneros dcpellere fcetus. 
Sic canibus cotulos similes, sic matribus hcedos 
Noram: sic parvis camponere magna solebam. 

This is a just picture of the analogical way of 
thinking. 



3SS OF THE HUMAN MIND. [CHAP. 7« 

But to come to the system of Des Cartes, 
concerning the human understanding: it was 
built, as we have observed, upon consciousness 
as its sole foundation, and with ideas as its ma- 
terials; and all his followers have built upon the 
same foundation, and with the same materials. 
They acknowledge that nature hath given us 
various simple ideas: These are analagous to the 
matter of Des Cartes's physical system. They 
acknowledge likewise a natural power by which 
ideas are compounded, disjoined, associated, 
compared: This is analogous to the original 
quantity of motion in Des Cartes' s physical sys- 
tem. From these principles they attempt to ex- 
plain the phenomena of the human understand- 
ing, just as in the physical system the phenomena 
of nature w^ere to be explained by matter and 
motion. It must indeed be acknowledged, that 
there is great simplicity in this system as well as 
in the other. There is such a similitude between 
the two, as may be expected between children 
of the same father: but as the one has been found 
to be the child of Des Cartes, and not of nature, 
there is ground to think that the other is so like- 
wise. 

That the natural issue of this system is scep- 
ticism with regard to every thing except the ex- 
istence of our ideas, and of their necessary rela- 
tions, which appear upon comparing them, is evi- 
dent: for ideas being the only objects of thought, 
and having no existence but when we arc consci- 



CHAP. 7.] CONCLUSION. 389 

ous of them, it necessarily follows, that there is no 
object of our thought which can have a continued 
and permanent existence. Body and spirit, cause 
and effect, time and space, to which we were 
wont to ascribe an existence independent of our 
thought, are all turned out of existence by this 
short dilemma: Either these things are ideas of 
sensation or reflection, or they are not: If they 
are ideas of sensation or reflection, they can have 
no existence but when we are conscious of them; 
if they are not ideas of sensation or reflection, 
they are words without any meaning. 

Neither Des Cartes nor Locke perceived this 
consequence of their system concerning ideas. 
Bishop Berkeley was tire first who discovered it. 
And what followed upon this discovery? Why, 
with regard to the material world, and with re- 
gard to space and time he admits the consequence. 
That these things are mere ideas, and have no 
existence but in our minds: but with regard to 
the existence of spirits or minds, he does not ad- 
mit the consequence; and if he had admitted it, 
he must have been an absolute sceptic. But how 
does he evade this consequence with regard to 
the existence of spirits? The expedient which 
the good Bishop uses on this occasion is very re- 
markable, and shows his great aversion to scepti- 
cism. He maintains, that we have no ideas of 
spirits; and that we can think, and speak, and 
reason about them, and about their attributes, 
without having any ideas oi' them. If this is so 






390 OF THE HUMAN MIND. [CHAP. 7. 

my Lord, what should hinder us from thinking 
and reasoning about bodies, and their qualities, 
without having ideas of them? The Bishop ei- 
ther did not think of this question, nor did not 
think fit to give any answer to it. However, we 
may observe, that in order to avoid scepticism, 
he fairly starts out of the Cartesian system, with- 
out giving any reason why he did so in this in- 
stance, and in no other. This indeed is the only 
instance of a deviation from Cartesian principles 
which I have met with in the successors of Des 
Cartes; and it seems to have been only a sudden 
start, occasioned by the terror of scepticism; for 
in all other things Berkeley's system is founded 
upon Cartesian principles. 

Thus we see, that Des Cartes and Locke 
take the road that leads to scepticism, without 
knowing the end of it; but they stop short for 
Avant of light to carry them farther. Berkeley* 
frighted at the appearance of the dreadful abyss, 
starts aside, and avoids it. But the author of 
the Treatise of Human Nature, more daring and 
intrepid, without turning aside to the right hand 
or to the left, like Virgil's Alecto, shoots direct- 
ly into the gulf: 

Hie specus horrendum, et sa>vi spiracula Ditis 
Monstrantur : mptoque ingens Acheronte vorago 
Pestiferas aperit fauces. > — 

4. We may observe, that the account given 
by the new system, of that furniture of the ho- 



CHAP. 7»] CONCLUSION. 3Q1 

man understanding which is the gift of nature, 
and not the acquisition of our own reasoning fa- 
culty, is extremely lame and imperfect. 

The natural furniture of the human understand- 
ing is of two kinds; First, The notions or simple 
apprehensions which we have of things: and, Se- 
condly, The judgments or the belief which we 
have concerning them. As to our notions, the 
new system reduces them to two classes; ideas of 
sensation and ideas of reflection: the first are con- 
ceived to be copies of our sensations, retained in 
the memory or imagination; the second, to be 
copies of the operations of our minds whereof we 
are conscious, in like manner retained in the me- 
mory or imagination: and we are taught, that 
these two comprehend all the materials about 
which the human understanding is, or can be em- 
ployed. As to our judgment of things, or the 
belief which we have concerning them, the new 
system allows no part of it to be the gift of na- 
ture, but holds it to be the acquisition of reason, 
and to be got by comparing our ideas, and per- 
ceiving their agreements or disagreements. Now 
I take this account, both of our notions and of 
our judgments or belief, to be extremely imper- 
fect; and I shall briefly point out some of its ca- 
pital defects. 

The division of our notions into ideas of sensa- 
tion, and ideas of reflection, is contrary to all 
rules of logic; because the second member ot 
the division includes the first. For, can we form 



392 OF THE HUMAN MIND. [CHAP. 7. 

clear and just notions of our sensations any other 
way than by reflection? Surely we cannot. — 
Sensation is an operation of the mind of which 
we are conscious; and we get the notion of sen- 
sation, by reflecting upon that which we are con- 
scious of. In like manner, doubting and believ- 
ing are operations of the mind whereof we are 
conscious? and we get the notion of them by re- 
flecting upon what we are conscious of. The 
ideas of sensation, therefore, are ideas of reflec- 
tion, as much as the ideas of doubting or believ- 
ing, or any other ideas whatsoever. 

But to pass over the inaccuracy of this divi- 
sion, it is extremely incomplete. For, since sen- 
sation is an operation of the mind, as well as all 
the other things of which we form our notions by 
reflection; when it is asserted, that all our notions 
are either ideas of sensation, or ideas of reflec- 
tion, the plain English of this is, That mankind 
neither do, nor can think of any thing but of the 
operations of their own minds. Nothing can be 
more contrary to truth, or more contrary to the 
experience of mankind. I know that Locke, 
while he maintained this doctrine, believed the 
notions which we have of body and of its qualities, 
and the notions which we have of motion and of 
space, to be ideas of sensation. But why did he 
believe this? Because he believed those notions 
to be nothing else but images of our sensations. 
If therefore the notions of body and its qualities, 
©f motion and space, be not images of our sensa- 



CHAP. 7.] i CONCLUSION. 39$ 

tions, will it not follow, that those notions are flot 
ideas of sensation? Most certainly. 

There is no doctrine in the new system which 
more directly leads to scepticism than this. And 
the author of the Treatise of Human Nature knew 
very well how to use it for that purpose: for if 
you maintain that there is any such existence as 
body or spirit, time or place, cause or effect, he 
immediately catches you between the horns of 
this dilemma; your notions of these existences 
are either ideas of sensation, or ideas of reflec- 
tion; if of sensation, from what sensation are 
they copied? if of reflection, from what opera- 
tions of the mind are they copied? 

It is indeed to be wished, that those who have 
written much about sensation, and about the other 
operations of the mind, had likewise thought and 
reflected much, and with great care upon those 
operations; but is it not very strange, that they 
will not allow it to be possible for mankind to 
think of any thing else? 

The account which this system gives of our judg- 
ment and belief concerning things, is as far from 
the truth as the account it gives of our notions 
or simple apprehensions. It represents our senses 
as having no other office, but that of furnishing 
the mind with notions or simple apprehensions 
of things; and makes our judgment and belief 
concerning those things to be acquired by coin- 
paring our notions together, and perceiving their 
agreements or disagreements. 



394* OF THE HUMAN MIND. [CHAP. 7* 

We have shown, on the contrary, that every 
operation of the senses, in its very nature, implies 
judgment or belief, as well as simple apprehen- 
sion. Thus, when I feel the pain of the gout in 
my toe, I have not only a notion of pain, but a 
belief of its existence, and a belief of some disor- 
der in my toe which occasions it; and this belief 
is not produced by comparing ideas, and perceiv- 
ing their agreements and disagreements; it is in- 
cluded in the very nature of the sensation. When 
I perceive a tree before me, my faculty of seeing 
gives me not only a notion or simple apprehen- 
sion of the tree, but a belief of its existence, and 
of its figure, distance, and magnitude; and this 
judgment or belief is not got by comparing ideas, 
it is included in the very nature of the percep- 
tion. We have taken notice of several original 
principles of belief in the course of this inquiry; 
and when other faculties of the mind are examin- 
ed, we shall find more, which have not occurred 
in the examination of the five senses. 

Such original and natural judgments are there- 
fore a part of that furniture which nature hath 
given to the human understanding. They are 
the inspiration of the Almighty, no less than our 
notions or simple apprehensions. They serve to 
direct us in the common affairs of life, where our 
reasoning faculty would leave us in the dark. 
They are a part of our constitution, and all the 
discoveries of our reason are grounded upon them. 
They make up what is called the common sense of 



CHAP. 7.] CONCLUSION. 395 

mankinds and what is manifestly contrary to any 
of those first principles, is what we call absurd. 
The strength of them is good sense, which is often 
found in those who are not acute in reasoning. 
A remarkable deviation from them, arising from 
a disorder in the constitution, is what we call 
lunacy ; as when a man believes that he is made 
of glass. When a man suffers himself to be rea- 
soned out of the principles of common sense, by 
metaphysical arguments we may call this meta- 
physical lunacy ; which differs from the other spe- 
cies of the distemper in this, that it is not conti- 
nued, but intermittent: it is apt to seize the pa- 
tient in solitary and speculative moments; but 
when he enters into society, Common Sense re- 
covers her authority. A clear explication and 
enumeration of the principles of common sense 
is one of the chief desiderata in logic. We have 
only considered such of them as occurred in the 
examination of the rive senses. 

5. The last observation that I shall make upon 
the new system is, that, although it professes t# 
set out in the way of reflection, and not ana- 
logy, it hath retained some of the old analogical 
notions concerning the operations of the mind; 
particularly, That things which do not now exist 
in the mind itself, can only be perceived, remem- 
bered, or imagined, by means of ideas or images 
of them in the mind, which are the immediate 
objects of perception, remembrance, and ima- 
gination. This doctrine appears evidently to 



396 OF THE HUMAN MIND. £CHAP. J. 

be borrowed from the old system; which taught, 
that external things make impressions upon the 
mind, like the impressions of a seal upon wax; 
that it is by means of those impressions that we 
perceive, remember, or imagine them; and that 
those impressions must resemble the things from 
which they are taken. When we form our notions 
of the operations of the mind by analogy, this 
way of conceiving them seems to be very natural* 
and offers itself to our thoughts: for as every 
thing which is felt must make some impression 
upon the body, we are apt to think, that every 
thin^ which is understood must make some im- 
pression upon the mind. 

From such analogical reasoning, this opinion 
of the existence of ideas or images of things in 
the mind, seems to have taken its rise, and to 
have been so universally received among phi- 
losophers. It was observed already, that Berke- 
ley, in one instance, apostatizes from this prin- 
ciple of the new system, by affirming, that we 
have no ideas of spirits, and that we can think 
of them immediately without ideas. But I 
know not whether in this he has had any fol- 
lowers. There is some difference likewise a- 
mong modern philosophers, with regard to the 
ideas or images by which we perceive, remem- 
ber or imagine sensible things. For, though 
all agree in the existence of such images, they 
differ about their place; some placing them 
in a particular part of the brain, where the soul 



CHAP. 7-] CONCLUSION. 3Q7 

is thought to have her residence, and others 
placing them in the mind itself. Des Cartes 
held the first of these opinions ; to which Newton 
seems likewise to have inclined; for he proposes 
this query in his Optics: " Annon sensorium 
" animalium est locus cui substantia sentiens 
" adest, et in quern sensibiles rerum species per 
"nervos et cerebrum deferunter, ut ubi, prae- 
" sentes a prsesente sentire possint?" But Locke 
seems to place the idea of sensible things in the 
mind; and that Berkeley, and the author of the 
Treatise of Human Nature, were of the same opi- 
nion, is evident. The last makes a very curious 
application of this doctrine, by endeavouring to 
prove from it, That the mind either is no sub- 
stance, or that it is an extended and divisible 
substance; because the ideas of extension can- 
not be in a subject which is indivisible and un- 
extended. 

I confess I think his reasoning in this, as in 
most cases, is clear and strong. For whether the 
idea of extension be only another name for ex- 
tension itself, as Berkeley and his author assert; 
or whether the idea of extension be an image and 
resemblance of extension, as Locke conceived; 
I appeal to any man of common sense, whether 
extension, or any image of extension, can be in 
an unextended and indivisible subject. But while 
I agree with him in his reasoning, I would make 
a different application of it. He takes it for 
granted, that there are ideas of extension in the 



398 OF THE HUMAN MIND. [CHAP. ?'. 

mind; and hence infers, that if it is at all a sub- 
stance, it must be an extended and divisible sub- 
tance. On the contrary, I take it for granted, 
upon the testimony of common sense, that my 
mind is a substance, that is, a permanent subject 
of thought; and my reason convinces me, that 
it is an unextended and indivisible substance; 
and hence I infer, that there cannot be in it any 
thing that resembles extension. If this reasoning 
had occurred to Berkeley it would probably have 
led him to acknowledge, that w r e may think and 
reason concerning bodies, without having ideas of 
them in the mind, as well as concerning spirits. 

I intended to have examined more particular. 
\y and fully this doctrine of the existence of ideas 
or images of things in the mind, and likewise 
another doctrine, which is founded upon it, to 
wit, That judgment or belief is nothing but a 
perception of the agreement or disagreement of 
our ideas: but having already shown, through the 
course of this inquiry, that the operations of the 
mind which we have examined, give no counte- 
nance, to either of these doctrines, and in many 
things contradict them, I have thought it proper 
to drop this part of my design. It may be exe- 
cuted with more advantage if it is at all necessa- 
ry, after inquiring into some other powers of the 
human understanding. 

Although we have examined only the five 
senses* and the principles of the human mind 
which are employed about them, or such as have 




CHAP. 7.] CONCLUSION. 399 

fallen in our way in the course of this examina- 
tion: we shall leave the further prosecution of 
this inquiry to future deliberation. The powers 
of memory, of imagination, of taste, of reasoning, 
of moral perception, the will, the passions, the 
affections, and all the active powers of the soul, 
present a vast and boundless field of philosophical 
disquisition, which the author of this* inquiry is 
far from thinking himself able to survey with ac- 
curacy. Many authors of ingenuity, ancient and 
modern, have made excursions into this vast ter- 
ritory, and have communicated useful observa- 
tions: but there is reason to believe, that those 
who have pretended to give us a map of the whole, 
have satisfied themselves with a very inaccurate 
and incomplete survey. If Galileo had attempt- 
ed a complete system of natural philososphy, he 
had, probably, done little service to mankind: but 
by confining himself to what was within his com- 
prehension, he laid the foundation of a system of 
knowledge, which rises by degrees, and does 
honour to the human understanding. New- 
ton, building upon this foundation, and in like 
manner confining his inquiries to the law of 
gravitation and the properties of light, per- 
formed wonders. If he had attempted a great 
deal more, he had done a great deal less, and 
perhaps nothing at all. Ambitious of following 
such great examples, with unequal steps, alas! and 
unequal force, we have attempted an inquiry 
only into one little corner of the human mind; 



400 OF THE HUMAN MIND. [CHAP. 7. 

that corner which seems to be most exposed to 
vulgar observation, and to be most easily com- 
prehended; and yet, if we have delineated it 
justly, it must be acknowledged that the accounts 
heretofore given of it were very lame, and wide 
of the truth, 



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